2000 problems are avoided. Some printed reports may show only a two digit year to save space. This is used to make sure that staff cannot make unauthorized transactions or see confidential information. This means assigning a password to each person that determines their access level. If you don't need passwords, you shouldn't be forced to use them.
Passwords determine the functions a person can use.
All sales transactions are logged with the date, time and name of the sales person. Option to require a manager's password before the system will void a sale. A training mode password where all POS functions can be used but no data is saved. This is used to undo the results of serious errors. For example, say you delete twenty invoices and then discover that they were the wrong twenty.