My counter runs on a Windows PC with a USB printer. Can the POS print on it?

Yes. Under Settings → The POS add a device of the kind A Windows PC that only prints, pair it with the six letter code in the GetMenu Print app on that PC, and under Settings → Printing & receipts add the printer as Installed on a Windows PC, which covers USB and any other printer Windows can see. The PC then prints the tickets and receipts sent to it, and an Android POS or a tablet can print on that PC's printer through it. It sells nothing and approves nothing. The POS and the counter tab in the docs describes the four kinds of device.