Hello, congrats on a successful siege! I will try to look around this, but I’m pretty sure it’s part of the Manor System which doesn’t really work in C3. I’ll let you know more after I look into this.
The tax rate is actually set, as you can see that items sold in Giran are actually 15% more expensive than any other town. I am not entirely sure why it doesn’t show in the castle tab correctly yet though.