I must admit that I fail to understand what this has to do with GDPR compliance. SalesAmounts are not considered information that relates to an individual. Moreover, you seem to be less concerned about the information that may ID an individual like a telephone number. Maybe it's a less than representative example, but you should also have a chat with your data protection officer first.
If it's the information itself that should be partioned into sets with different access/visibility-settings, then I fail to understand why you want to hide it behind a series of password-like stars, and not just eliminate a part of the information altogether if a particular SalesManager shouldn't have access to it. Section Access, combined with Data Reduction is ideally suited for the latter. And on top of that, it's not too complex to implement and easy to manage without changing anything except for the data (e.g. your data) that controls Section Access.