I drove pretty close to the reverse of that route last year but it was CA to RI. WI to Rushmore is quite a haul plus you're passing a beauful stop in the badlands. Stop at the Badlands for the night. Spend half a day there and then go to Rushmore. Check out Custer State Park for wildlife if that interests you.
Windcave NP is also right there but GPS will mess you up and a map isn't much help either because you can't find the visitor center. Just call the visitor center for directions before you go. You need a half day but you have to book a tour since it's a cave.