On arrival at the airport in Zanzibar is very essential to draw Cash at the ATM there as there no ATMs outside Stonetown, Paje and Nungwi.
ATM at the Zanzibar Airport. Just after arrivals and steping out the door into the world beyond and in sight of the taxi stand, immediately turn around. ATM is to the right of the exit door on the outside building. No guarantees that it will actually work though.
I would suggest you have a 10$ note for your taxi in to town if you can not get your currency at the Zanzibar Airport, you can get it in Stone town.
ATM In Nungwi, Zanzibar is next to the Nungwi Police Station checkpoing with maximum redraw limit is 400,000 Tanzania shilings (180$) for one transaction. Incase you need more Cash you can redraw several times.
ATM in Paje, Zanzibar is near by United Petroleum, close to the Paje Police Station checkpoint.
You can not withdraw Foreign currency form ATM machines, drawing USD is the only place to draw Cash in USD is inside Barclays which is 1.6km from Stone town, Malawi road close to Bank of Tanzania.
Also we would advise you to bring USD notes with you no older than 2013 because Older is difficult to exchange in Tanzania.