Using a Modifier/Upsell at last screen in POS

Hi would it be possible to use the API to make a modifier for an upsell on the final screen on standard POS? Whether on the iPad reader or terminal? See image attached on this screen. I’m trying to build an app for the marketplace (or easy to integrate API) for merchants that lets users round-up spare change from their purchase.
Square_Stand2-600x422

:wave: At this time the ability to add a round up functions to sales on the Square app isn’t currently available. :slightly_smiling_face: