The Nicaragua's currency is the Cordoba, it borned in 1912 in honour of Francisco Hernandez de Cordoba one of the spanish captains that conquested Nicaragua. In the common language it is called peso.
You can find coin of ½, 1 and 5 Cordoba and bill of 10, 20, 50 and 100 Cordoba. You can also find banconotes for hundredth part of Cordoba, but you can't buy a lot of things with these banconotes. For the most part in Nicaragua you can indifferently pay by Cordoba or by dollars. You can also use credit card like VISA, America Express e Master card.
In the city of Managua you can find automatic cashes besides supermarkets and petrol pumps however is better going to the banks. The Bank of Central America offers good and cheaply services as regards automatic cashes. The change cordoba/dolares is fixed by Banco Central; now is 22.9 Cordobas for 1 dollar.
Till now there is'nt an official exchange for european money so it is better travelling with american dollars. If you travel with Central America's Country currency usually you do not have problems to change your currency at the Nicaragua's border or at the airport's offices
When you are in Nicaragua you can change currency at the bank or, if you have rush, you can find in the street people (called "coyotes"), witch change dollar in Nicaragua's currency, the rate is similar at bank's rate.
All banks offer the change operations with a rate equal at the official rate, the only problem is the long queue witch you can find at the cash desk. The best time do this operation is after lunch.