Using nopCommerce 3.90:
When signed in as an Administrator, viewing a product on the front-end always shows the price excluding tax.
I have tried Configuration > Settings > Tax settings > "Allow customers to select tax display type" checked and unchecked, with the "Tax display type" set to "Including tax" and there is still no change.
Viewing the same product page as a guest or authenticated customer (not Administrator) shows the price correctly.
I have tried looking through the source code and, so far, have been unable to find a reason why the price is always shown excluding tax when signed in as an Administrator