Yeah, data corruption is a big issue with the Pis, and definitely not something you want on a Point of Sale.
In my head it would be booting into Chromium to run an offline web app, and the app would make requests against a CouchDB service on the local network. No transaction data would be written to the Pi's memory.
This is all just spitballing though. I'm literally just considering it.
True. If I need a lof of writes, I hook up an SSD. Also, For some applications, you can roll your own root file system and mostly avoid writes. I.e. Yocto