The currency in Iran is the Iranian rial. Coins are available in denominations of: 50, 100, 250, and 500 rials, while banknotes come in: 100, 200, 500, 1,000, 2,000, 5,000, 10,000 and 20,000 rials.
Iran also has another unit of currency which is Toman (a sub unit), 1 Toman is equivalent to 10 Rials. Thanks to the rapid inflation, Iranians often use Tomans and this is how they count money but it is always better to ask before giving your money to someone which unit they are saying. Sometimes people say just "5" or "5,000" for the same 50,000 Rials. Toman is more common in oral quotes, while Rial is the official unit and used in most verbal documents. Price etiquettes may come either in Rial or Toman and usually are understood by the buyers. In case of doubt, check it with the seller. It is quite confusing and you might feel you are cheated but don't worry, eventually you will get used to it.
Do not change money on the street, as this practice is illegal in Iran. Although many shops and hotels display a Visa logo in their window, in practice, credit cards are rarely accepted in Iran, with the exception of some of the larger hotels. This makes it essential that you have some ready cash at all times. Money can be exchanged at the airport on arrival or at banks and exchange offices (“sarrafi”) throughout the country. Banks are open from Sunday to Wednesday, 07:30 to 16:00; Thursdays, 07:30 to 12:00; and closed on Fridays.
Although Iran has a functioning network of ATMs (cashpoint machines), they can only be used with locally issued bank cards, so are useless to travellers unless you open a local account.