I used the SunTrust Delta SkyMiles Platinum Visa debit card to pay over $40K in taxes. I should receive over 40K Delta SkyMiles for a fee of only $3.89. The Terms & Conditions provide that internet purchases qualify and no exception is listed for payments of taxes:

*SunTrust SkyMiles® Check Cards are available with any SunTrust personal or business checking account. The annual fee is $20 for the SkyMiles Classic Check Card and $55 for the SkyMiles Platinum Check Card and SkyMiles Business Check Card. The one-time Enrollment Bonus of 10,000 miles for the Platinum and Business Check Cards; and 5,000 miles for the Classic Check Card is a limited-time offer from 4/01/2010 – 6/30/2010. The one-time Enrollment Bonus Miles will be awarded after the first signature-based purchase with your Classic, Platinum or Business Check Card. The first signature-based purchase must be made by 07/31/2010 to be eligible for the one-time Enrollment Bonus Miles. Only signature-based purchases, Internet purchases, phone or mail order purchases or automatic bill payments qualify for mileage earnings. Cash advances, ATM transactions, payments for stored-value cards and purchases made with a PIN do not qualify. Please allow 6-8 weeks for Enrollment Bonus Miles to be credited to your SkyMiles account. The one-time Enrollment Bonus Miles are only available to new SunTrust SkyMiles Classic, Platinum and/or Business Check Card customers and cannot be combined with any other enrollment offer. The SunTrust personal or business checking account must also be open and in good standing at the time the Enrollment Bonus Miles are awarded. All SkyMiles program rules apply. To review the rules, please visit delta.com/skymiles.
The SkyMiles Check Cards are issued by SunTrust Banks, Inc., and the cards are available in AL, AR, FL, GA, MD, MS, NC, SC, TN, VA, WV, and DC.