It is not expected to tip taxi drivers and as the prices here in the Fethiye area (like the Dolmuses) are substantially higher than elsewhere in Turkey don't tip.
If you have a transfer (not by taxi) then the driver is likely to be on a wage and probably a low one so if they drive carefully and they are pleasant and helpful then it would be nice to give a tip.
Tipping for meals and good service is about 10%.