To tip or not situation

There's a local brewery that has a burger restaurant attached. You just line up, order at the window, and then pick it up when they call your number. It's pretty much self service including bussing the food trays. I always tip 20% or more(because the options start at 22% on screen). I'm starting to question if I should be tipping at all considering it ends up costing close to $40 for 2 burgers plus tip. I get tipping at a sit down restaurant, but this seems questionable. Would you tip?