Dominican law requires hotels and restaurants to add a 10% service tax to your bill (in addition to the 16% sales tax).  Sometimes bills will show this 10% under a label that reads "Ley" (law).  

If asked, managers will say that "service is included" while employees will say "tips are not included".  Here is why their answers differ:

The 10% service tax is not a TIP to your server, cleaning lady, etc.  It is distributed among ALL employees but not necessarily in equal parts.  In many establishments, a large part of the 10% goes to managers not to the bartender, cook, cleaning lady, receptionist, etc.   Moreover, in establishments were the 10% is equally distributed among all employees, the person you had contact with may only get a mere fraction of what you are charged if, for example, the establishment has 20 employees (that is, 5% of your 10%).

Some establishments, however, recognizing that the tax does not encourage good service and that customers should be able to tip at their discretion, decided not to include this 10% service tax (despite the legal requirement).

Tips thus are highly appreciated by those who provide good service and are in direct contact with customers.