The attendant at one of the main toll booths told me that if you only do that once, don't worry about it. I ran into that problem leaving MCO one night at the $1.00 exact change booth and I didn't have a dollar in silver. I tried to pay it at the manned booth and that's when she told me the above.
The thing that could get you is if you are in a rental that has violated the tolls several times, then the rental company will send you the bill.