I've been trying to get better about using the "Price Paid" and "Shipping Paid" fields recently. Once I started making a habit of it the paradigm shift with most online retailers now collecting sales tax occured.
It would be useful to have a separate field for "Taxes Paid". This would allow folks like me trying to track their spending better to do so more accurately while (theoretically) maintaining the integrity of the "Price Paid" field. The same toy here in NC at retail price costs a consumer 6 to 7.5% more than it would for our pals in NH, OR, etc so I didn't want to start lumping that in with "Price Paid" and skew those numbers.
Not a bad idea. I've thought about requesting it, too. I raised it up the flagpole, now let's see if the generals salute it.
So far nobody seems to object, but it'll probably have to wait until a few other major projects get sorted out. KidTDragon opened an issue in our tracker, so it's in the 'ol system. Stay tuned...