The currency in the Republic of Ireland is the euro (€). The island's peculiar political history means that the six Ulster counties that make up Northern Ireland use the pound sterling (£). Although notes issued by Northern Irish banks are legal tender throughout the UK, many businesses outside of Northern Ireland refuse to accept them and you'll have to swap them in British banks.
Hotels €1/£1 per bag is standard; gratuity for cleaning staff at your discretion.
Pubs Not expected unless table service is provided, then €1/£1 for a round of drinks.
Restaurants For decent service 10%; up to 15% in more expensive places.
Taxis Tip 10% or round up fare to nearest euro/pound.
Toilet Attendants Loose change; no more than 50c/50p.