I set the permissions for my model, the access denied comes from the field sale_ids because the base user doesn't have sale rights.

Gotcha, then yes you would have to put the permission for sales on the base user group. It may be better to create new permissions and add those to the base user and sales group respectively. I.e. base users have a permission to read this module, while the sales group can read and write.

Thank you (sorry can't mark as a valid answer)

So I need to give read permission on sales to the users in my custom module group

I believe so!