The last time I bought ammo from Walmart was a long time ago, but the clerk asked me the same question, and I said, "None of your business." Then she said she couldn't sell me the ammo if I didn't choose, and I asked to speak to her supervisor. Supervisor comes over, and I say to him, "I don't think I should be required to declare what I'm going to shoot this ammo out of." He turns to the clerk and says, "Just punch in "rifle" and get on with it." He walks away, she punches in "rifle", I pay the total and down the road I go.
They know it's stupid, but their company requires it.
Parker