There are several situations in Romania in which tipping is appropriate, such as in restaurants, hair salons, hotels, and taxis. Employees in restaurants earn very little in their wages, so you should always tip them if the service has been good, but should not feel obligated to tip if the service was unsatisfactory. Tips of between 5 - 10 % are normal in restaurants.
It is also nice to leave a tip for the hotel maids, and leaving a tip of about 4 lei a day will likely make your stay more pleasant. Also, if the hotel concierge or porters go out of their way to help you, a tip is appropriate, of between 2 -15 lei, depending on what they do for you.
Tips for hairdressers, masseurs, etc. are usually between 10 - 15 % of the bill.
As a rule, taxi drivers do not expect to be tipped, but if they are courteous and professional, a tip of 5 % is normal, or more if they do something extra to help you. When paying for a taxi, wait for the driver to give you your change, even if you plan to tip, and then pay him his tip.
Strangely, it is also expected to tip nurses and doctors in hospitals. Often you will need to tip a nurse before you can get anyone to treat you.