A tip in Latin America is generally given to reward good service but it is not mandatory as it is in the United States. Usual practices may vary from country to country, even within regions in a country, but the normal guidelines apply.
If you feel a particular tour guide, waiter or host has done a good job then they will greatly appreciate a little something extra. As a guide we recommend 10% of the bill for restaurants and US$5-15 per day for a tour guide.
In some places like Brazil, Ecuador and Mexico a service charge will be added to the bill. However, this generally will not go to the waiters themselves.
A tip is a propina in Spanish, gorjeta in Portuguese.