Good choice. You can read the entire TM discount policy on the intranet HR site, I think it's also on the Target Pay & Benefits site under the TM discount information. You can buy gifts -- actual things you are giving away for free -- but don't try combining this with a discount (or tax exemption) belonging to someone else.
Depending on your state's laws, there are some not-for-profit and non-profit organizations which can register for tax-exempt status.
Another tax-exempt category which I've run across on a handful of occasions are foreign diplomats; the US State Department allows foreign consular personnel bearing State Department diplomatic ID to make tax-exempt purchases. As Seattle is a major US city with a pretty high number of foreign consulates, we used to see these diplomatic purchasers occasionally, but not as frequently nowadays.