South Dakota only says you have to have proof of paying sales tax. If you pay tax in Iowa or wherever, they are fine with that as long as you have a receipt to prove it. If you figured out how not to pay tax anywhere, then they won't let you register in their state without you paying them. Pretty straight forward. Their 4% is less than Iowa so would be bargain. When I went to renew mine last week in South Dakota, they told me that future 1st time registrations have to be made in person because the employees are tired of getting calls from out state people who get paperwork back when not filled out complete and call and b****. Can still do renewals by mail once get plate.