I always put a US $20 away in a safe place just for my exit fee. Then I don't spend it or worry about trying to round it up on the day I'm leaving.
Second last trip, I couldn't find the safe place, so assumed I'd spent it and ended up having to cash another traveller's cheque to have the cash for my fee. What a drag on my last day.
Happily on my last trip, I found the secret compartment and so didn't have to worry about it at all that time.
What did I learn? Always use the same secret compartment.