That's illegal, not refunding the tax on a purchase refund. I've had a few of my own returns from local retailers not include a refund of the tax, a quick request to the supervisor fixed it without any hassle [Toys R'Us tried it twice].
I've also had a couple of quotes in which I inquired more deeply into, as they added tax to the shipping charge...I've been meaning to investigate that, as only a select few tried that, and it didn't appear to be a State issue, as others in the same areas did not do the same. Tax fraud isn't exactly what a legit reseller should play with.
DIM POST, STUPID
POST = INPUT $X
STUPID = PEEK 420, 255
IF POST >= STUPID, THEN GOTO H3LL