The Tanzanian Shilling is the official currency of Tanzania, but $US are also widely accepted in tourist areas. Dollar notes printed before 2009 are usually not accepted. You can exchange money at many authorised dealers, banks and bureaux de change. Get a receipt after each transaction.
Most banks in major cities have ATMs, but they are not always reliable and sometimes break down or run out of money. To minimise the risk of card cloning, only use ATMs located within the bank. Travellers cheques are not widely accepted and non-Bank of England sterling notes may be subject to less favourable exchange rates.