The practice of giving a tip is not usual in small restaurants, taxis, and motorbikes. However, tipping the waiters, porters, maids, drivers, and guides is appreciated elsewhere in the world, but this should relate to the pleasure felt by the guest. The tip helps the service staff eke out their somewhat meager income.
But in general, Tipping is optional in Nepal however, this is in the rising phase.
If you have been served well, give a 10% tip at restaurants if a service charge is not included. You may wish to round this up to 10% plus loose change. A hotel porter and the room maid is also happy to find a small financial token of appreciation after your departure. The amount is dependent on the category of hotel and length of stay. If in a beach hotel you wish to give an amount in the first few days, this will be highly appreciated, the rest can be given at the end of your stay.
13 % VAT is on all goods and services which includes meals and rooms. And any expressway toll needs to be paid also separately.