JQuery round off money / currency to 2 decimals

Question

How do I round off a money amount to two decimals using the arithmetic convention that

167,7451 is rounded to 167,75

12,1819784 is rounded to 12,18

Notice I want to do it arithmetically and be returned a float and not a string so simple formatting solutions are not what I'm searching for.

So far I found the following:

amount = 167.7451;
rounded = (amount.toFixed(2));
alert(rounded);

however the result of toFixed() is a string, so if I need to do more calculations I need to parse the string to a float again.

The .toPrecision method instead wants to know how many digits I need so to round the amount to two decimals I'd need:

amount = 167.7451;
alert(amount.toPrecision(5));

that's ridiculous because I'd need to first know how many digits I have before the decimals.

Answer 1

167.7451 is rounded to <span class="result1"></span>
<br>By adding 10 result is: <span class="result2"></span>
<br>By adding rounded 0.254999 result is: <span class="result3"></span>

<script type="text/javascript">
    window.jQuery(document).ready(function($){
        function my_round(num) {
            return Math.round(num * 10 * 10) / 100;
        }

        var amount = 167.7451,
            amount1 = my_round(amount),
            amount2 = amount1 + 10,
            amount3 = amount2 + my_round(0.254999);


        window.jQuery('.result1').text( amount1 );
        window.jQuery('.result2').text( amount2 );
        window.jQuery('.result3').text( amount3 );
    });
</script>

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Updated code should work.