jQuery Rounding Number To Nearest Interval Such: 0.05, 0.5, 0.1, 5, 10, 100

JSFIDDLE LINK ||| TEXT LINK

Html Content:

<input type='text' name='number' style='width: 150px;' value='10.21'/>
<input type='text' name='round' style='width: 50px;' value='0.25'/>
<input type='text' name='dp' style='width: 50px;' value='2'/>
<input type='button' name='check' value='Check'/>
<div></div>

jQuery Content:

var div = $("div");
log("---------------------------------------------------------");

$("input[type='button']").click(function() {
    var number = parseFloat($("input[name='number']").val());
    var round = parseFloat($("input[name='round']").val());
    var dp = parseFloat($("input[name='dp']").val());
    if (!isNaN(number) && !isNaN(round) && !isNaN(dp)) {
        var nn = roundInterval(number, round, dp, "up");
        
        log("<br/>Rounding: " + numberToString(number, dp, true) + 
            " using: " + round + 
            "/" + "<span class='up-down'>Up</span>" + 
            " as: " + numberToString(nn, dp, true));
        
        var nn = roundInterval(number, round, dp, "down");
        
        log("<br/>Rounding: " + numberToString(number, dp, true) + 
            " using: " + round + 
            "/" + "<span class='up-down'>Down</span>" + 
            " as: " + numberToString(nn, dp, true));
        
        log("---------------------------------------------------------");
    }
});
$("input[type='button']").trigger("click");

function roundInterval(number, interval, round, roundType) {
    if (round > 9) {
        round = 9;
    }
    else if (round < 0) {
        round = 0;
    }
    number = number > 999999999999999 ? 999999999999999 : number;
    var isMinus = false;
    if (number < 0) {
        isMinus = true;
        number = number * -1;
    }
    number = parseFloat(numberToString(number, round));
    interval = parseFloat(numberToString(interval, round));
    var multiplier = roundType == 'up' ? Math.ceil(number / interval) : Math.floor(number / interval);
    
    log("Multiplier: " + multiplier);
    log("As: " + number + "/" + interval + " :: " + (number/interval));
    
    number = multiplier * interval;
    
    number = multiplier * interval;
    if (isMinus) {
        number = number * -1;
    }
    return parseFloat(number.toFixed(round));
}

function numberToString(number, dp, asDp) {
    var format = '#';
    if (asDp === undefined || asDp == null) {
        asDp = false;
    }
    if (dp !== undefined && dp != null && !isNaN(dp)) {
        if (dp > 9) {
            dp = 9;
        }
    }
    else {
        dp = 0;
    }
    if (dp > 0 && asDp) {
        format += ".";
        format += "0000000000".substr(0, dp);
    }
    else if (dp > 0) {
        format += ".";
        format += "##########".substr(0, dp);
    }
    number = number.toString();
    var minus = number.substr(0, 1) == '-' ? '-' : '';
    var ln = "";
    if (number.lastIndexOf("e+") > -1) {
        ln = number.substr(0, number.lastIndexOf("e+"));
        for (var i = ln.length - 2; i < parseInt(number.substr(number.lastIndexOf("e+") + 1)); i++) {
            ln += "0";
        }
        ln = ln.replace(/[^0-9]/g, '');
        number = ln;
    }
    var tail = format.lastIndexOf('.'), nail = number.lastIndexOf('.');
    if (nail < 0 && tail >= 0) {
        number = number + "." + format.substr(tail + 1, 1);
        nail = number.lastIndexOf('.');
    }
    tail = tail > -1 && nail > -1 ? format.substr(tail) : '';
    var numtail = number.substr(number.indexOf(".") ) ;
    if(tail.length > 0 && dp !== undefined && dp > 0) {
        tail = tail.substr(0, dp + 1);
        var tails = tail.split(''), ntail = "", canPop = true;
        for (var i = 1; i < tails.length; i++) {
            if ((tails[i] == '#' || tails[i].match(/([0-9])/g)) && numtail.length > i) {
                ntail += numtail.substr(i, 1);                    
            }
            else if(tails[i] == '#') {
                ntail += '0';
            }
            else {
                ntail += tails[i];
            }
        }
        var ttail = ntail.split(''), ptail = tail.substr(1).split('');
        for(var i = ttail.length - 1; i > -1; i--){
            if (ptail[i] == '#' && canPop && (ttail[i] == '0' || ttail[i] == '#')) {
                ntail = ntail.substr(0, ntail.length - 1);
            }
            else {
                canPop = false;
            }
        }
        if (ntail.length > 0) {
            tail = "." + ntail;
        }
        else {
            tail = "";   
        }
    }
    number = number.replace(/\..*|[^0-9]/g,'').split('');
    format = format.replace(/\..*/g,'').split('');
    for(var i = format.length - 1; i > -1; i--){
        if(format[i] == '#') {
            format[i]=number.pop()
        }
    }
    number = minus + number.join('') + format.join('') + tail;
    return number;
}

function log(m) {
    div.prepend(m + "<br/>");
}