Hi,
1- Go to International -> Localization
2- Import the localization pack of your country
3- Go to International -> Taxes -> Tax Rules
4- Click on the + sign at the top right to create a new Rule
5- Create a Tax rule according to your needs, and click on ENABLE
Make sure that...
At the bottom of International -> Localization -> Taxes you have set Enable TAX to YES and Display tax in the shopping cart to YES (click on save)
This is how I made it work.