A tip plays a part in the compensation for the hard work your team on the mountain do and should always be based on the quality of service provided.
It's common for trekkers to encounter crew members who go the extra mile. While tipping is based on service quality, those who stand out—like head guides, waiters, personal porters, and others— can sometimes receive a slightly higher tip as a token of gratitude.
Avoid discussing the subject of tipping with your crew, except with your head guide if you have any specific questions. It is best to clarify about tipping in advance of your arrival to Tanzania.