When I see a tip jar that I don't think is merited I simply don't leave anything in it. However, I don't normally mind them at take out places and pick-up counters because I don't believe the employees have any expectation of a sizable tip, just whatever people feel they can spare. I usually just leave ten to fifty cents. When I worked at a bakery in high school which had a take-out counter, we placed a tip jar out and divided it up equally every week. We almost never got bills and we didn't expect them. It was just an outlet for someone who wanted to show their thanks with their change.