The OP makes a valid point, but for most players, the difference is chump change. If we are talking a stack of items for 40 gil each @ 5% tax: 4158 gil vs a stack of items at 41 gil each with no tax: 4059... that's a difference of 99 gil. For some people, scrolling down to find the lower price, checking the difference, etc is not a great expenditure of time, over 100 gil.