It is not obligatory to tip in hotels or for other services. But be generous to a point (please do not overdo it as some Brazilians will think that every gringo is a walking bank). Just keep in mind the minimum wage in Brazil is around 1100 reais a month, so a little money helps a lot, especially the poorer people. If you park your car in one of the many public car parks you will find that it is most likely a “territory” of a group of people that consider the place their place of work. They will help you to park and unpark, “guard” your car and sometimes even wash it for you for an additional fee (R$35-50). You do not have to give them anything, but a 2 real note will not go astray and will help someone to support his family.