DEAR MISS MANNERS: Is there a correct way for a customer to act at the checkout counter? I usually stay silent, except to answer and return pleasantries if the cashier offers them. I occasionally glance at the total and assist in bagging if the cashier is alone. I have had similarly quiet cashiers; often, the only exchange during the whole process is “Have a nice day” and “Thanks, you too.” I work in retail myself, and I despise the empty cheeriness and how draining it can be during a long shift. So I figure that giving the cashier a quiet respite is not unwelcome. I also glance around rather …