The 10% service tax is NOT a TIP but is required by law as a way to insure that a SALARY for the service staff is collected. This has been beat to death on this forum by cheapskates that would stiff a waitress even in their home countries. However, if you feel that your service warrants it, by all means leave some sort of a tip on the table. You'd be suprised how far a $20 to $30 peso gratuity will go in assuring good service the next time you visit the restaurant.
Yeah, some winter residents are notoriously noted in Florida restaurants for not tipping..."eh".
$100 pesos is roughly $3USD right now....as a rule, in the States, I drop 20% of the bill as a tip unless the service is horrible ($1 for every $5 on the bill)....
I chose to maintain the standard when I was last in the DR and it didn't take long to be remembered or to insure that I got GREAT service...and a smile.
On the day I left, a handshake and a big GRACIAS from my favorite waiter....wanna bet my table will be waiting for me when I get back?
Tip on the food and drinks if you need to scrimp (don't tip on the taxes in other words)....but by all means.....take care of those who make the DR a great place to be.
Goes back to the old saying, "Treat people how you want to be treated."