Configuration

For setting access to each user, go to Settings --> Users and select point of sale user.

Select the POS Users tab and set the Allowed POS for this user.

Allowed POS

Now when the user logs in, he can see only the Allowed POS in his dashboard.

POS as Administraton

For Managers set point of sale as Administrator.

POS without restriction

Administrator can see POS without restriction. He can also see the allowed users for each POS if the option-show allowed users is set.