Non deductible VAT (Iva Indetraibile) is a specific kind of tax that represents a cost for the company. They shouldn't appear in the tax report but they need to be visible in the invoice. 

Here you find the proper configuration in V15: 

In this way, these taxes won’t appear in the tax report (in so far there are no “tax grids” selected and the “tax closing entry field” is unchecked). Moreover, there’s no account associated with them, meaning that they will go directly to the goods purchase account. Here below you find the journal items related to invoices that contain this tax.