My two cents.

Dear customers -

You just spent what I make in an hour on a cup of coffee.  You come into my store every day, sometimes twice a day, and you know exactly how much that beverage costs.  Somehow, you don't seem to have figured out that the container sitting on the counter is our tip jar.  If you don't want to tip us, that's fine - you aren't required to do so.  It's your prerogative.   But for fuck's sake, stop using the tip jar as your own personal "Take a Penny" dish.  If you're short by a couple of cents on occasion, I understand.  It happens to the best of us, and in that situation, it really isn't a big deal.  But every single fucking day?  We're all fucking sick of it.  Just for that, I'm Crazy Gluing a penny to the floor, for the sole purpose of watching you try in vain to retrieve it.  Don't be a dick.

Signed,
Your disgruntled, depressingly underpaid barista.