Okay Guys, after hours and hours, I KNOW HOW YET!

1) Go to POS>Products>Products, and create your new product or modify your existing product, Define the Sale Price as you want it to appear for your customers. And define its Customer Taxes as " 7.7% Sales" ( It will apply 7.7% excl. on your price by default but don't worry, at the end, it will be modified)

2) Then go to POS>Configuration>Setings>POS, go to Accounting section, Activate the  Flexible Taxes, then save it! after that, go again to this same section and click on Fiscal Positions.

3) In there, you can create 2 new positions: one "Dine-In", and one "Take Away". During the creation of both, you have to configure your fiscal position as

(if Dine-In)

Tax Mapping>Tax Product : 7.7% Sales (Sales)
Tax Mapping>Tax to Apply: 7.7% Sales (incl.) (Sales)

(if Take Away)

Tax Mapping>Tax Product : 7.7% Sales (Sales)
Tax Mapping>Tax to Apply: 2.5% Sales (incl.) (Sales)

4) Go back to the POS>Cofiguration>Setings>POS>Accounting section, and select your default position (Take-Away or Dine-In that we created before) and in the "allowed" section below, write both, Take Away and Dine-In. It will display on your User interface POS (when you selecting the product for your order) a Button with the icon of a book, when you click on that, you can choose the taxe( take away or dine In) to apply to your order.

You're WELCOME!