You're looking for toFixed:

var x = 4.3455;
alert(x.toFixed(2)); // alerts 4.35 -- not what you wanted!

...but it looks like you want to truncate rather than rounding, so:

var x = 4.3455;
x = Math.floor(x * 100) / 100;
alert(x.toFixed(2)); // alerts 4.34