Help with javascript rounding

There is no built-in rounding function to Acrobat forms. One can use the util.printf to create a string with the decimal round or some methods of JavaScript. But I think the best approach is to create a function that can round both the decimal value or whole number of a value.

Such a document  function could be:

function myRound (n, d)
{
// souce D.P. Story, Phd.
    n = String(n).replace(/,/g,"");
    d = -1*d
    var m = Math.pow(10,d);
    n *= m;
    n = Math.round(n);
    n /= m;
    d = ( d > 0 ) ? d : 0;
    n = n.toFixed(d);
    return Number(n);
} // end my round function;

One then can add a line to the end of a field's Custom JavaScript calculation like:

event.value = myRound(event.value);

Or is one of the other 2 calculation options are used, then for the Validation use a custom script like:

event.value = myRound(event.value);

sample invoice

Also note that when one applies the rounding can have an effect on the result. If computing sales tax, round the input values for the calculation and then round the result.

I would round the values being summed to come to the subtotal before computing the sales tax.

You need to correctly round each intermediate value. You can do this if you use a custom calculation script for each calculated field, but can't if you use one of the other calculation options. As an example, here's a custom calculation script that sums three field values:

// Custom calculation script

(function () {

    // Get the three input values, as numbers

    var v1 = +getField("Text1").value;

    var v2 = +getField("Text2").value;

    var v3 = +getField("Text3").value;

    // Calculate the sum

    var sum = v1 + v2 + v3;

    // Round to the nearest 100th and set this field value

    event.value = util.printf("%.2f", sum);

})();