National currency is the Tanzania-Shilling (TSH). US-Dollars are also used commonly. Small amounts are usually paid in TSH and larger amounts in US-$, as the largest TSH bill is 10.000 Shilling (approx. 8 Dollar/6 Euro). You can change Euros or US-Dollars in Tanzania to Shilling. Store your receipts as you have to present them when changing Shillings back to your foreign currency when leaving the country. It is not allowed to take Tanzania-Shillings out of the country. Money can be changed also at banks and Foreign Exchange (Forex) Bureaus, but never change money on the streets, as it is illegal and highly probable you get cheated.
You can get cash from banks also using your EC-Card. Upper class hotels and restaurants accept international credit cards.