A POS system needs to be created. A customer comes to the cashier and the
cashier takes items from the cart and enters the item ids into the system. For
each item type, the system asks the number of items to be purchased. The
system creates a bill and adds line items to it. At the end, the total is
calculated and the tax should be added. The system should ask to enter the
amount of money the customer would give. The system should print the entire
bill with the balance to be given back to the customer.