Is there already some module which allows to point a connected device (tablet, Raspberry Pi or similar) to an URL which shows the the products being scanned and the total to the customer's side? I know that a LED pole display can be added but a bigger LCD screen could show more information to the client.

If there is not I was thinking about programming something on my own: I have experience with Javascript and PHP and through some AJAX calls I could achieve what I need. Which files generate the actual HTML of the POS module?