Yes, Findaway, that was perfect. As I see, you ran into that in the past. Thank you so much for the explanation! I'll quote the pertinent part of what you wrote on that previous thread here...
I'm looking at flying one of the new international non-stops out of MDW on WN and ran into a taxes savings by booking a round-trip instead of separate one-ways... Specifically, the "+Transportation Tax (International)"...is charged on the return only if it is a one-way flight and is not charged on the return if the reservation is booked as a round-trip.