Coins:

Although the official unit of currency in Iran is the Iranian Rial, Iranians usually talk in terms of Tomans, a unit equal to 10 Rials. As a general guide, in writing, prices are given in Rials and prices quoted in conversation are in Tomans. Since people usually omit to say what units of currency they are talking about, you need to make absolutely sure whether you are either talking Rials or Tomans before agreeing to a price? One Toman is worth ten Rials.
Also, sometimes the Bazaaris and the shopkeepers in the Bazaar will often omit the denomination of high prices and say for example two Toman as shorthand for 2000 Tomans (IR20000) or even 2000000 Tomans (IR20000000).
Coins are issued in values of 50, 100, 250, 500 and 1000 Rials with banknotes produced in 100, 200, 500, 1000, 2000, 5000, 10000, 20000, and 50000 Rial denominations Bank notes are easy to read, as the numbers and names are printed in Farsi and English. However, coins are only in marked in Farsi and Arabic numerals.
Changing money is available at the bank in the airport (upon arrival to Iran), bank in cities (big cities is recommended), official money exchange offices or street rates at the streets. A better compromise is the private exchange offices (sarāfi) scattered around most large cities and major tourist centres. Although their rates are comparable to those of the banks, they are far quicker and, unlike their black market colleagues, they can be traced later on if something goes wrong.
US dollars and Euros are the most useful and widely-accepted currencies, Also new and large (USD 100 or EUR 100 or higher) bills in good condition are preferred and usually get a better rate.
Due to U.S. sanctions, no body can not use credit cards, Although MasterCard is accepted in some places, and so, bringing enough cash is strictly recommended. ATMs exist in most cities, but only Iranian customers, who have local bank cards and some cards from Arabian countries are accepted and are useless to travelers unless you open a local account.