Tipping in Tanzania is not expected, but certainly appreciated.  If you feel that the quality of service you have received is good, then it is now customary to leave a tip to show your appreciation to those who have served or guided you. 

For guides, a guideline of US$10 per person per day is reasonable.  For servers, a guideline of US$5-$10 per day is reasonable, depending on the establishment and the service.  Since food is often included in the price of the lodges, it may be difficult to calculate a 10-15% tip on the bill.  For porters, US$1-2 per bag is reasonable.

Though crime is not very high in Tanzania, flaunting your excess money is never a good idea and there isn't any need to reinforce the rich Westerner stereotype.