Everything in Developer mode ! 

In the configuration settings of the website you can select, display tax excluded or tax included but unfortunately you can not do both. 

When you change this all of your users are moving from the access right group Tax display B2B to Tax display B2C or the opposite. 

Those groups seem to be useless because there is nothing in those except notes but in the standard code when a user is in one of those groups it will change his way to see prices in ecommerce.

To display prices tax included for non logged in users: 

1. Set in website configuration : Tax excluded 

2. On the group : Public users, in the inherited groups : 

1. Delete Tax display B2B

2. Go on the group Tax display B2B : Delete in users, those that are user type = Public, in standard, normally there is only “Public user”.

3. Add on Public group the inherited group : Tax display B2C

Now, someone who’s not logged in will be considered as a public user and will see prices tax included thanks to this group.