Just as a followup in case other people are interested, LTS now sells a RS232-to-IP converter that will allow you to hook up a POS easily to any LTS NVR that supports the POS function.
http://www.ltsecurityinc.com/accessory-ethernet-tcp-ip-converter.html
LTS DVRs/NVRs also have a smart search function now that allows you to search the video clips by transaction and view the playback clip of said transaction.