SO fiddle

Test Fiddle mainly for SO Questions

by Nick Craver

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/overcast/jquery-ui.css">
Type a number in me! <input type="text" class="amount-text" />

JavaScript

$(".amount-text").bind('change',function () { 
     $(this).val(function(i, v) { return parseFloat(v).toFixed(2); });
});