Agreed that you should take it to an airport. I've never done this with Dollar but I've changed the return with Hertz/National/Avis. Typically the daily/weekly rate changes (sometimes SIGNIFICANTLY), other times it's a drop fee of up to $250. In any event, I've never been turned away when trying to give the car back.
Depending on the emergency issue, and if you have travel insurance, they might help out (either contacting Dollar and/or reimbursing any fees).
Good luck!