Point of sale with fidelity cards

I would like to build a point of sale with mvd but i don't know where to start or how to do it properly. For example i would like to scan the product with a barcode scanner and add it to a grid and save that receipt somewhere. The fidelity card works in the following way , the customers receives for example from the total sale 5% back and in the end when it has enough money he can use it to pay for merchendise. The app must have an inventory , a customer database , the fidelity card has a barrcode on it so on the initial sale the card must be scanned. I know that there is a point of sale on this forum but it doesn't meet requirements.