Point of Sale, (POS) can be quite different for different types of businesses with different workflow and inventory management requirements. The invoices starter solution that comes with FileMaker might serve as one starting point, though I'm not impressed with how it attempts to manage inventory levels.
But perhaps you need to be able to scan barcodes: Need help writing script to integrate barcode scanning
and you may want an integrated approach for managing sales and updating your inventory simultaneously: Managing Inventory using a Transactions Ledger
But those are still only parts of a possible whole as some POS systems also control other devices such as the cash drawer or can scan and process credit/debit card transactions.
Thanks for taking this on. I'm guessing that the pos on an IPad is basically just a data screen with touch screen activated buttons instead of a mouse pointer to log the choices?
Essentially. It also addes additional issues to resolve if you need to scan bar codes or print hard copy receipts. Both are possible but the details differ and the link I suggested for barcodes will not work with an iPad as the technology needed for scanning barcodes will be different.