AVYCON's series of Plug & Play recorders with current firmware will support the ability to bring in data/text from most POS registers and allow to overlay the readout from a register on top of live video, and even allow for searching for items or events that occurred. The most basic requirements are that the POS register must allow for text output either out of an RS-232 serial port or via TCP/IP.
Below is a link for a PDF guide detailing how to connect most POS systems to our recorders: