I got this idea because I use the mod COT (http://www.nexusmods...ion/mods/6441/?), really like it, but I thought there was a better way, so look at that mod first as background info for what I want to do.
-Any time a septim is added to/removed from your inventory invisible, weightless "gold" (vanilla coin(s)) of appropriate quantity are added to/removed from your inventory.
-In the barter menu, merchants still deal in the vanilla "gold" (renamed to "septim(s)"), however when "gold" is removed copper/silver/gold septims are added to the merchant's inventory (first auto-stores gold septims (puchase price/100 (rounded down)), second it stores silver septims (remaining amount/25 (rounded down)), third it auto-stores the rest in copper septims.
-Same method in reverse when you are selling items (and receiving payment).
Edited by HyperManFZ, 11 May 2017 - 12:35 AM.