Error displaying price without tax in checkout

-- HikaShop version -- : 3.0.0
-- Joomla version -- : 3.6.5
-- PHP version -- : 7.0
-- Browser(s) name and version -- : FF 51.0.1

We have imported with a CSV file thousands of products (variants included). Everything is fine. The system is setted to show prices with tax and correctly it displays the price with tax in the product page or in the modules.

Anyway in the checkout process the prices are not displayed with tax but WITHOUT tax!

It's not a template related isssue (same issue with Protostar)

We have made another test creating a test product frombacked (not importing it) and in this case the product during the checkout process is displayed with the correct price WITH tax, meanwhile the products we imported via CSV are always displayed WITHOUT tax.

We made then another test on the product test we created via backend: set the product price using the column instead of the dot (100,95€ instead of 100.95€). In this case also the product test created in backend, during the checkout pricess, display the price WITHOUT tax.

What's wrong?
Thanks in advance.