I only tip for sit-down restaurants where an actual servers brings me my food
everywhere else I preemptively give the stank face as I mash the 'no tip' button on their payment system
I usually just round up to the next $5 amount to make the numbers clean, don't really care what the % is
so a $16.83 bill gets a $3.17 tip
this makes it easier to plan a meal budget, like "ok I'm spending $20 on a burger and fries today"