Math.round with checkbox for tax

Question

I have a form that needs to calculate sales tax. If it ships to California, then tax is applied.
I have been attempting to cobble together a Boolean JavaScript in Acrobat v8 (on a Mac) using Math.round(). No luck, it always defaults to else. I have searched this forum, planetpdf, bought Padlova's Acrobat Forms book, and just have been stonewalled on this issue.
I have a series of items that SubTotal - ItemTotal.1, ItemTotal.2, ItemTotal.3 using the simplified Value is menu.
California tax is calculated with (Tax * SubTotal) * 0.0725, where Tax is a checkbox with a Mouseup value of 1. When the checkbox is active, the tax is added, otherwise the tax value is zero.
As near as I can tell looking at the State Board of Equalizations tax tables, Acrobats default rounding is displaying the correct amount of tax.
Is there any reason I shouldnt leave this as it stands, as opposed to more research into the correct syntax for Math.round() with a checkbox variable?

Answer 1

Interesting - but exactly the sort of thing a programmer hates. It
gives a huge table, but it doesn't give the exact rules needed to
actually write legal code.
There isn't a generic standard to use. In fact, in some states, the
rule changed. For example, in 2005, Ohio changed to "The computation
shall be carried out to three decimal places. If the result is a
fractional amount of a cent, the calculated tax shall be rounded to a
whole cent using a method that rounds up to the next cent whenever the
third decimal place is greater than four. A vendor may elect to
compute the tax due on a transaction on an item or an invoice basis."
Instead of "always rounding up in any case where the tax calculation
yielded any fractional amount over a whole cent".
But you say "rounds up". Let's test that with the table. $100 is a
good starting point. 7.75% of $100 is exactly $7.75, so no rounding is
needed. This matches the table, which says that amounts over $99.93
pay $7.75 tax. So, what about $99.93? Calculated exactly, 7.75% is
$7.744575. If this were simply rounded up, the tax would be $7.75.
This suggests it is actually rounded to the closest, and might be the
same as the new Ohio rule. Or some variation on it.
Interestingly, there is a California sales tax calculator on
http://www.csgnetwork.com/salestaxcalc.html, and it seems to match the
table. They do offer a JavaScript calculator for license, and given
that it runs to something like 60 lines of code, this may be worth
considering, as reimplementing it (without copying) sounds hard work.
Aandi Inston