POS and receipt printers manufacturers provide procedures to install their devices in RDS environments which are specific in terms of communication speed / print format (...) 
Moreover, port COM are usually preferred to USB as it supports a wider range of hardware.

To redirect port COM you will need the procedure issued from your device manufacturer to deploy on a RDS / terminal server environment - which is very similar to TSplus. 

Open a client generator, click on the "Local resources" tab, and check the COM ports :

You can also enable the COM port redirection using standard RDP client by editing its properties as show below :

For example, you may need to change the communication speed between server on client for COM mapping depending on the settings of your POS application. This is done in your device manager (devmgmt.msc) :