I have zero PHP experience and unfortunately even less time.
I have however managed to hack together an addon providing a tax exempt
function that does not use discounts, thus avoiding any one penny errors.
I believe there is a desire for this function and would like it to be available for
others to use, I simply am not able/willing to provide any support for it.
I will gladly submit it to the downloads if it is Ok to provide addons without
support from the contributer. I am also open to turning it over to someone
with PHP experience who could proof the work and wants to take it over.