Expect all public offices to be closed on the following days. Also remember that Nicaraguan holidays are subject to decree, shutting the banks down without warning to suit some politician’s inclination.
Like the rest of Latin America, every single town and city has its own patron saint whom the residents honor each year with a prolonged party that lasts 1-3 weeks. These fiestas patronales combine holy religious fervor with the consumption of alcohol in biblical proportions. Most celebrations include include Virgin and Saint parades, special masses, fireworks, cockfighting, rodeos, concerts, gambling, dances, and show-horse parades (hípicos). Many towns have additional celebrations of specific events in their history.
Semana Santa (or Holy Week) is the biggest celebration of the year, occurring during the week leading up to Easter Sunday. The weeklong vacation sends most city folk to the beach for sun and debauchery (and usually a couple of drownings, too) while shops close their doors and everyone takes a breather.
In popular beach areas like San Juan del Sur [1], expect hiked prices and few vacancies. In other areas, you may also encounter altered bus schedules and other travel annoyances.
Links:
[1] http://www.moon.com/destinations/nicaragua/southwest-coast