My shop is not open yet. But I have extensive knowledge on how these big box stores work. Yes, your are doing a rotation for free, but, it opens up other avenues for revenue. You take those tires off and you get to look at the brakes. Check the suspension, look at bushing, etc. People hear free and they take advantage of it, but it gets people in the doors. As far as profit in tires, there is not much. 20% at most and thats for the cheaper tire.
When we open, I will not offer a free rotation with tires bought from me, I will offer a free rotation with my oil change. It takes me 2 minutes to do, and I do it while the oil is draining. I make it habit to roll the tire to the other end of the car and look for nails or any foreign object. Feathering of tires , etc. If I see something, I spray it, If it leaks , I notify customer. They are happy I picked up on it before it became a problem and now I just made money on a quick tire repair.
This is how these big box stores survive, upselling and upselling quick services. Wipers, tire repairs, bulbs, belts , alignments. Free is not always free, you will make money some how. I laugh when I see ads for a $60 brake job, it's to get people in the door. Once there in a $60 brake job becomes $300. It's not a bait in switch its, clever marketing. $60 was just for a pad slap, but than you factor in the caliper thats hanging up, the warped rotor and so on.