I've received parking tickets in Germany and just because I didn't want the rental company adding on any administrative fees for billing me later on, I paid them on the spot at the local police station.

Last week I ran a toll gate in Florida - I had no change, there was no attendant and there was no where to turn around. I asked at the rental car desk if I needed to be concerned about it and she said no, they usually just issue a warning the first couple of times.