By default Cartweaver is set to standard tax option. However enabling VAT is very easy.
Just follow these simple steps.
Go to admin -> Store Setting -> Tax settings.
Once you click on the Tax settings you will see Tax / VAT option by default Tax is selected in the drop down.
You need to select VAT and click save settings. After which you will be able to see options regarding VAT.
Important to remember, the VAT amount would only be shown in the cart if you are logged in on front end as user.