How to set auto 2 decimal number in input type=“text” in javascript

var zzz = parseFloat(numb).toFixed(2)

&&

function updateCost() {
    var amount = parseFloat(document.getElementById("amount").value),
        delivery = parseFloat(document.getElementById("delivery").value),
        total = amount + delivery,
        fixedrate =  total / 100 * 8.2,
        grandtotal = fixedrate + total;

    document.getElementById("total").innerHTML = total.toFixed(2);
    document.getElementById("amountdiv").innerHTML = amount.toFixed(2);
    document.getElementById("deliverydiv").innerHTML = delivery.toFixed(2);
    document.getElementById("grandtotal").innerHTML = grandtotal.toFixed(2);
    document.getElementById("fixedrate").innerHTML = fixedrate.toFixed(2);
}

$(function(){
    document.getElementById("amount").onchange =
        document.getElementById("delivery").onchange = updateCost;
});