Note, the tax I'm referring to is the tax we all pay when we put things up for sale and they get bought. The buyer may also pay a tax depending on what city they or your retainer may be in but you as the seller must always pay the selling tax of the city your retainer is in. The tax theoretically can change from city to city (I think it's to even out how many retainers are in each and the actual amount of each city's sell tax can be checked with the retainer hiring NPC) but it's usually 5% and is clearly stated at the bottom of the price setting screen of every item you put up for sale. For example, a 100k item will give the seller 95k when it sells (5k goes to tax) while the buyer will pay 100k/105k (5k-10k goes to tax from their end) depending on if they're in the city the retainer is in or not, and the intercity tax doesn't affect what the seller gets either.