(Math.round(num * 100) / 100).toFixed(2);

Live Demo

var num1 = "1";
document.getElementById('num1').innerHTML = (Math.round(num1 * 100) / 100).toFixed(2);

var num2 = "1.341";
document.getElementById('num2').innerHTML = (Math.round(num2 * 100) / 100).toFixed(2);

var num3 = "1.345";
document.getElementById('num3').innerHTML = (Math.round(num3 * 100) / 100).toFixed(2);
span {
    border: 1px solid #000;
    margin: 5px;
    padding: 5px;
}
<span id="num1"></span>
<span id="num2"></span>
<span id="num3"></span>

Note that it will round to 2 decimal places, so the input 1.346 will return 1.35.