My only exception to the “pre-discount” price is when places have a “buy 1 get 1” deal and they try to make you tip based on that, but the single item price is way overpriced because of it. Happens around me a lot where they’re like 3pack tacos, buy 1 get 1 $21, like yeah that’s great price for 6 small tacos, but I wouldn’t be paying $21 for 3 tacos, so I’m not gonna tip whatever crazy amount for a bill that “would have been” $75 or something for some tacos and a drink. Granted these are usually carry out orders, but don’t try to artificially inflate my bill to get better tips because you discounted it to a lower price.