It's easy then, what you do is you include the ITBIS, and the propina legal within the price. for instance if you want to sell a beer at $100 even, its price before tax would be about $79 (that is what you sell it, the additional $21 are tax + service, for a total of 26%). If you have a POS system you can program it into your pricing to display the tax, or you can just display totals. Its important to remember, that if the bar sells 100 pesos, taxes and service in, the emplyees don't get 10, but rather 7.93 pesos. And it is by law, there is no ifs or buts about it. The only exception I can think of is for take out orders, but that's all.
Basically if you include all taxes in the price, you devide sales by 126 parts, 100 is for the business, 16 are for taxes, 10 are for employees. 10/126 =0.794 if you were wondering where i got the number from.
Personally i think that including the taxes is better, it doesnt leave a bad taste in a clients mouth when they are hit with an unexpected 26% on their bill. And it is good to state this on your menu, that prices are as seen, AI, if you will.
Next thing you'll need to figure out is how to divide and pay the %. Usually management will get the largest amount, followed by Chefs (in the case of restaurant), Bartenders, waiters, kitchen staff, cleaners - some other staff might get a small bonus.
The logic is this, managers(good ones) will make a big impact on sales, they will attract clientele, prevent theft (can be huge in DR), maintain quality - it is also norlmal to offer managers sales based incentives for reaching sales targets. Bartenders will have a higher salaray, and receive more propina legal, because their access to tips is less than that of wait staff. etc.
If i've left anything unclear, feel free to PM, or I can clear it up in here, its a little late.