Accepting Only Two Characters after decimal point in JavaScript or jQuery

How to do validate a textbox to accept only two characters after decimal point in jquery or javascript

function isNumber(evt) {
evt = (evt) ? evt : window.event;
var charCode = (evt.which) ? evt.which : evt.keyCode;
if (charCode > 31 && (charCode < 48 || charCode > 57) && charCode != 46) {
return false;
}
else {
var len = document.getElementById("<%=txtAmount.ClientID%>").value.length;
var index = document.getElementById("<%=txtAmount.ClientID%>").value.indexOf('.');
if (index > 0 && charCode == 46) {
return false;
}
if (index > 0) {
var CharAfterdot = (len + 1) - index;
if (CharAfterdot > 3) {
return false;
}
}
}
return true;
}