Most likely it stands for impuestos incluidos, or "taxes included". The increase from the base amount to the "i.i." amount is 23%, which includes both the IVA (a value-added tax) and a gratuity for the server:
A notable question came from a reader named Stacy who told us about the time she dined at a nice restaurant in Quepos and she asked the waiter to bring the check:
“OMG, what is this 23% Costa Rica tourist tax?”
That 23 percent you saw on the receipt from the restaurant does not entirely represent taxes. Only 13 percent of the meal price was assessed on value-added taxes (Impuesto al Valor Agregado, or IVA in Spanish). The remaining 10 percent was allocated to the waiter’s tip. It looks like the restaurant did everything correctly, particularly if it itemized and indicated the IVA tax and tip separately on the bill.
Credit:stackoverflow.com‘