From the Settings (Admin Interface -> Taxes -> Settings) menu:
Enable tax on Site Fees
If checked, enables tax for site fees.
Select the tax that will be applied to site fees:
Allow Sellers to Apply Tax
If checked, allows sellers to apply tax on their listings.
The selected tax will be automatically applied to site fees based on user location.
To see if the tax is applied to site fees go to Tools -> Accounting and select an invoice:
Example: See below how to find taxes (the tax corresponds to the VAT tax described in the Configuration menu)