Unless your employee account has the Limit To Shop setting configured to a specific shop, you can process sales from any of the shops and registers in your Retail account. Once a register is selected, all sales will be associated to that register until you switch registers.
From the main menu, tap Manage Registers.
If you have a multi-store account, tap your desired shop.
Tap the register you'd like to process sales in.
NOTE: If the selected register is not currently open, you'll be asked to submit the opening count for the register. For more information, please see our Opening and closing cash registers on your iPad.