One of my constant pet peeves during my time in Singapore was that ATMs dispense S$50 notes, but you get a lot of complaints when you use them to pay for a S$5 taxi ride. (Singapore has a S$10 note, but no S$20 note -- a gap that needs filling, in my opinion.)

My first stop after hitting the ATM was generally to a grocery store to buy something small. Starbucks worked well for this, too.