This used to be fairly widespread a long time ago. There used to be fares that are restricted for sale only in a certain country's POS (I believe these are still alive in ATPCO) but not really used anymore.

I remember examples of round-trip ticket A-B-A costing $x in A, $x/2 in B (plus another fare for country C) for some city pairs, but I don't think this has really been a thing in a decade at least.