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. 

Since food is often included in the price of the lodges, it may be difficult to calculate a 10-15% tip on the bill.  

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.

Outside of tours, tipping is not generally required for other services such as taxis, barbers and restaurants. If service is very good at a restaurant, you may conside rounding the bill to a convenient amount. The locals will not tip in restaurants. If someone offers to help you in shopping or purchasing bus tickets, etc, they will most certainly be compensated by the shop so a tip is not required.