exchange rate, but used that for street treats. Not much of a tipping culture (appreciated but not really done too much, maybe more for tours and stuff, but can add through CC or in dollars). We had a car, so didn't need it for taxis or anything.
But overall, use an ATM in the country (Schwab fee-refunded debit card is nice). Don't use their conversion rate, choose the option in colones and let the bank give you a better rate.