The local currency is Tanzanian Shilling (Tzs). Many hotels require payment in US$, in particular for accommodation, but also for food and drink and for tours. Taxis and car rentals are also paid in US$. You do need Tzs if you go shopping in the villages or eat at local restaurants (recommended!) and for petrol if you rent a car. Tzs come in notes of 10,000, 5,000, 2,000 and 1,000 shillings. Coins used here are 500, 200, 100 and 50 Shilling.
The Zanzibar Government closed all exchange bureaus on the island a while ago. One can only exchange money at the local banks, their new exchange bureau outlets and at the Post Office in Shangani.
The exchange bureaus inside the airport arrivals and departures halls are open 24/7. A CRDB exchange bureau is at the airport parking lot. Bring $100 and $50 notes for best rates. NB: latest news is that only US$ notes printed after 2013 will be exchanged!
For an indication on current exchange rates check https://crdbbank.co.tz/exchange-rates/
The bigger hotels, restaurants and car rentals have credit card facilities. A surcharge of 5% is applicable. Be aware that at many places credit cards are not accepted.
ATMs: You can only draw Tzs against your credit card or a card with a Visa or Mastercard logo. Two ATMS are at the airport parking lot, there are a few other ATMs in Stone Town. ATMs have a maximum payout of Tzs 400,000 per withdrawal. You can use your credit card multiple times until your daily withdrawal limit on your credit card is reached. You might have to visit different ATMs though.
The majority of ATMs are in Stone Town, these are the ONLY locations of ATMs outside of Stone Town (beware, they frequently run out of money!):
Paje: An Absa ATM is at the UP petrol station close to the police checkpoint. A NMB ATM is at the Petro Petrol station. Two more ATMs (Exim and Moja/PBZ) are at the roundabout.
Nungwi: A Barclays ATM is close to the UP petrol station just outside Nungwi on the main road
Dunga: A NMB ATM is between Dunga and Koani (central Zanzibar)
Petrol costs Tzs 2165 per liter for Super (May 2021) and is paid in Tzs. You can also pay in US$ but you’ll get a really bad exchange rate.
Simcard/internet: You can buy a simcard at the airport, with 12 GB it apparently costs US$ 20 (please note: all service providers increased their prices drastically early April 2021, I do not have any info about the current cost of the simcard). Zantel has the best coverage on the island.