How to round correctly in JavaScript

precise_round.js

function sign(num) {
	// IE does not support method sign here
	if (typeof Math.sign === 'undefined') {
		if (num > 0) {
			return 1;
		}
		if (num < 0) {
			return -1;
		}
		return 0;
	}
	return Math.sign(num);
}

function precise_round(num, decimals) {
	var t=Math.pow(10, decimals);
	return (Math.round((num * t) + (decimals>0?1:0)*(sign(num) * (10 / Math.pow(100, decimals)))) / t).toFixed(decimals);
}


precise_round(1.275, 2); // 1.28
precise_round(0.035, 2); // 0.04
precise_round(0.045, 2); // 0.05