Make her strip.

"You must remove all your clothes" you command, with new-found confidence in your voice. As you had hoped, the busty cashier immediately obeys, pulling her sweater up over her head and letting her sizable breasts tumble out. Noticing the lack of a bra, you reach out and attempt to squeeze her enormous tits, but she recoils in shock. "This is all normal." you quickly assure her, as you continue to play with her boobs. She stands completely still whilst you fondle her, occasionally moaning slightly when you rub her nipples. You eventually release your grasp and pull out your cock, and the blonde awkwardly shuffles back to fumble out of her remaining clothes until she stands before you, red-faced and completely naked.