Tags are free for residents here, but we usually split all the costs. Gas, camper costs (if we have one), group food, etc. Even the times the other person didn't have a tag (i.e., not enough residency time in AK) I still split the meat as long as they contribute equally (or more!).
I thought it sounded too generous to split evenly if the other costs weren't divvied up as well. Your system sounds right.