Prova questi...

<SCRIPT LANGUAGE="JavaScript">
<!--
x=4.52-4
alert(x.toFixed(2))
alert(x.toPrecision(2))
//-->
</SCRIPT>

<script>
Math.round(cifra*100)/100;

esempio:
var cifra = 6.6699;
var aa = Math.round(cifra*100)/100;
--
aa = 6.67
</script>