specific tax by category

[smpconseil]

Hello here is my problem I would put a tax only applies to a single category (virtuemart 2.0.18a). That is to say that whatever the number of items ordered in this category it is applied to this supplement.
In taxes and calculation rules I choose just a single category yet taxte this applies to all my products even if they are not in the selected category. Thank you for your help. I searched the forum but my English is not good and I did not found.
thank you very much


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