I just went back and checked 10 of my last rentals against the receipts and 1 of them was off by $21 and some change.

When I called in and asked billing about it, they said that because I returned the car to a different location, they did not have the full itinerary so they under charged me. She was nice about and credited me back the money. So anytime you rent from one location and return it to another there is a higher probability that your final "estimate" may be wrong....FYI.