You can implement this with the help of JavaScript.

function checkDecimal(val) {
	if (val.length >= 3)
		if (/\d*\.\d\d$/.test(val))
			return true;
		else {
			alert("Only two decimal places allowed");
			return false;
			}
	}

<input type="text" name="decimal" onKeyPress="return checkDecimal(this.value)">