The local currency in Tanzania is de Tanzanian Shilling. To see the current rate of the Tanzanian Shilling you can use this Currency Converter.
As you most probably won’t get Tanzanian Shillings in your home country it is easier to bring US dollars for your holiday. You can pay almost everywhere with US Dollars and in most accommodations and souvenir shops they will charge you in USD as well. Creditcards are accepted in some places, but often with high extra charges (+5%). You can use the ATM in Tanzania. This is however only possible in the bigger cities. In the safari parks and on the beaches of Zanzibar you won’t see them so be aware that you have enough cash money with you on these days.