Windows Embedded

One common use of Windows Embedded is for retailers on their EPOS devices, Windows Embedded 7 POSReady is ideal in this scenario, however I am not clear whether the POSReady stuff is in the Windows 8 version, although it does seem to be in "Windows Embedded 8.1 Industry"

Windows Embedded Industry - Wikipedia
Windows Embedded Products

One area worth studying is Microsoft POS for .NET Overview which explains what Microsoft offer in the world of POS, quoting the article:

POS for .NET is Microsoft’s implementation of the industry’s Unified Point of Service (UPOS) version 1.8 standards, for the .NET platform. POS for .NET is also backward-compatible with existing implementations of UPOS on the Microsoft Windows platform, named OLE for Point of Service, or OPOS.
The detailed documentation is available from POS for .NET v1.12 SDK Documentation and POSReady 7 Technical Reference (POSReady 7)