In Ireland, the currency is the Euro which uses the following symbol (€). Each Euro consists of 100 cents. Notes are issued in €5, €10,€20 €50,€100,€200 & €500 amounts although you will rarely find anything above €100 notes in local shops or restaurants.
Both Scotland & Northern Ireland share the same currency as both countries are apart of the UK. This currency is the British Pound Sterling, divided into 100 pence to every pound and the symbol for sterling is as follows (£). Notes are issued in £5, £10, £20, £50, £100 (allow £100 notes are very uncommon).
The two currencies are separate and not interchangeable. You cannot use US dollars or other foreign currencies in Ireland. Sometimes near the border of Northern Ireland & the Republic of Ireland shops, restaurants and pubs will accept both Euro & British Pound Sterling.