You can take whatever size paper tender you like. How much you exchange is up to you. Bringing a bunch of $20's or $100's is fine. If you want certain size bills just ask the attendant, and if they have them available they will give you some. I always like using the cambio on the West End, which is called Banmarc(sp). They have two separate enclosed stalls where nobody can see you doing your business. They have a little parking lot out front where you ride can wait and it is a short walk from there to inside the building, so no hassle to worry about.