I tip to-go coffee shop orders (when there are clear tipping norms, as is the case at all the coffee shops I go to). You can call the POS system an "accident of technological convenience", but it is also a prominent, clearly legible sign expressing the expectation that you're going to tip.

It is less of a big deal to stiff a coffee shop than a restaurant (you might actually get yelled at at a restaurant!) but if you talk to them when the shop is quiet they'll mutter under their breath about the regulars who don't tip.