Open Source Point of Sale has Employee Management built in. Each employee is given a separate Username and Password.
From the Employees tab, the Manager can grant and restrict access to the system's modules.
For instance, here Jane Test, a cashier, has been given access to the Sales and Customers modules. She can ring up sales and manage customers, but can't create inventory items or add suppliers. Somebody else will be given that job and, thus, access to those modules.
The system also has Employee Reports built in. You can print off Graphical and Summary Reports of your Employees that tell you which employees sold the most and were the most profitable. You can even export this information to Excel.
There is also a detailed Employee Report that shows you information about a specific employee for each of their sales. This includes Sales ID, Date, Items Purchased, Customer Name, Totals and Profit, Payment Type, and Sale Comments. There is even a link to the actual receipt, in case you want to dig further into a particular sale. You can also export this information to Excel as well.