I made sure to tell them 'Have a nice day'. If I got Merry Christmas in return, I would return that. If I didn't so what. But at least I tried to make sure every customer had a good experience at the store, even if they came in upset. You can call that spreading Christmas cheer in a small way, you can call it being kind to my fellow man. I am quite sure that's a bit more important to the intent of Christmas and to the spirit of Christianity than whether or not in a retail job one is allowed to use the 'right' salutation.
And as a former retail worker, I would ask that those that shop this year take a moment to be kind to the salesperson. Don't go off on a rant about how a company is not allowed to say Christmas. Wish them one anyway. Do it with a smile (instead of the constant scowl I am envisioning on some 'conservatives' and their feeling of being slighted). If you can't do that, at least tell them to have a nice day. It may not pay off for you, but it will for the next customer. Take a minute and exhibit the spirit of Christmas even if some store can't say the right words.
"Take a minute and exhibit the spirit of Christmas even if some store can't say the right words."
Standing ovation over here!