Tax for everyone Prestashop 1.6.1.1

[Simply123]

I'd like to find out if its possible to set Prestashop to show the including price for EVERYONE who logs into the site - regardless of location please.  I've searched many threads and followed the advice on many of them, but on certain browsers, the products still show as excluding.    None that I've found give advice on only one setting for everyone.

I have set my visitors price as the including VAT price, so all visitors see the correct price regardless. It causes confusion when customers login and a product is, for example, R100 (showing as tax incl, because that's how its been set) but its actually the excluding price.  The when the product is added to the cart, its R115 as 15% VAT has been added on.

Its not consistent though - sometimes it shows including, sometimes it shows excluding - its seems its dependent on the browser used. I use Edge - yesterday everything showed correctly, now today its showing excluding prices after login.  I've known Chrome to show the prices excluding in the past.  I have to run through all the settings almost on a daily basis to correct what customers see.  At times its difficult to convince customers why there are differences in the price.

We do not sell out of South African borders, so all our sales need to be inclusive of 15% VAT.  

This is what I've double-checked so far:

Customer Groups - set to show inclusive price

Localization - Localization - Set Language from Browser - NO

                                               - Set default Country from Browser Language - NO

                                               - Default Country is South Africa

Localization - Tax Rules set to 15%

Localization - Tax set to 15%

Is there a permanent setting I can change, or code I can add, to force the including VAT price to show for everyone that logs in, regardless of which browser they are using, or where their server is?