I thought the TiW auto-tip was calculated from the pre-discounted amount, has that changed? Cheshire Figment's example a few months ago, here. I'm also assuming that FL still has 6.5% sales tax.
In the OP's scenario ($88.95, $15 of which is alcohol):
TiW = 71.16 (20% off 88.95) + 4.63 (tax...