Many worlds don't use any currency at all, and instead the residents prefer using the barter system. Trading physical goods is commonplace throughout Remnant. Many stores will take either currency or goods, such as food. That being said, there is a currency, although not a physical one. There are no coins, bills or any other form of physical money, instead it is completely digital.
The name for the currency is Universal Resource Unit, and like its name implies, it is technically the only form of currency in the universe. The name is of course shortened in common use; most people call the currency URU (oo-roo).
The URU is roughly equivalent to 100 times the modern USD or CAD (US and Canadian dollar is pretty equivalent now too). And it most closely resembles the Japanese Yen, because the amounts are generally high as they don't have cents.
(EXAMPLES!!!) So, if a SMG (9 mm sub-machine gun) costs about $700 today, it will cost about 70,000 URU (there is a sign, like the $, but I don't have it on my keyboard!) If you for some reason wanted to get some 5 cent candies from a candy store, they would cost 5 URU each. So, in a very rough sense; 1 URU=1 cent. 100 URU=1 dollar. This might be different depending on the place you are, the demand/supply and just general over/under pricing that happens. Got it? Good.