Still, a physical tip jar tells me "a person actually working here put this here intentionally", while a POS sometimes (probably irrationally) makes me wonder if these were just the defaults Square or competition shipped the thing with, an A/B test on proposed amounts run by a faceless corporate board etc.
If you're paying a service charge, you're not expected to tip. (I know, this is annoying; the most annoying thing here though is the service charge).