I'm trying to make my own HTML5 POS using Square. My plan is to use Google's chrome.* APIs to handle a USB receipt printer and cash drawer. Square needs to be accessed via Java, which is what I am hoping to do by wrapping the Chrome app in an Apache Cordova container (if that's what they're even called) to make the app Android-compatible, also making them available to side-load on Chromebooks.
My biggest question is what chrome.* APIs are available on mobile these days? The last update was apparently July 2014... Please tell me there have been updates since then. Because if the chrome.usb API isn't available, I'm SOL and I'll basically need to rely on Java for Square's processing AND the receipt printer and cash drawer, and I don't know Java so that would be fun..not. Unless I'm missing something from Square's documentation on their API; perhaps it handles receipt printing and a cash drawer still. It didn't seem like it though.
The instant you need to talk to hardware your options got very limited.
If you need to have the Android device talk to the printer & drawer that would be over USB and then you would have to write at least part of the app in Java or find/write a Cordova plug-in which will handle the USB side.
If Android is only a partial requirement: how about local webserver on a PC to control the receipt printer and cash drawer via USB with Android serving as a client (pure web app/progressive web app, hybrid, or pure Java).
For Chromebooks, you would need to see how well the external hardware (USB) interfaces work as I've heard mixed results.