I for one either mentally multiply by 1.1 for an upper bound or don’t bother at all, mostly the latter, because (a) different items can be taxed differently; (b

I for one either mentally multiply by 1.1 for an upper bound or don’t bother at all, mostly the latter, because (a) different items can be taxed differently; (b) different states (sometimes even different cities) have different tax rates. For the record I hate it because I only care about the out-of-pocket costs. Same goes for tips.