It wouldn't be a best practice to isolate the POS environments from all the other internal systems. Pricing, items, taxes, offers, coupons, etc. are all separat

It wouldn't be a best practice to isolate the POS environments from all the other internal systems. Pricing, items, taxes, offers, coupons, etc. are all separate systems on the corporate network. They all need to communicate to the POS. It isn't realistic to air gap the POS at a business the scale of Target. PCI rules just state the cardholder data environment (CDE) needs to be segmented from the rest of the corporate network (in addition to many other obligations). That would usually be done with VLANs and firewalls, but both are still on the same layer 2 network.