What's a good way to reply when someone says "Have a blessed day"?

I get that salutation instead of “have a nice day” or “thanks for coming” at a lot of stores, usually said by a cashier or a server.

Except I don’t want their religion’s blessings. I don’t want blessings at all.

Would it be terribly gauche to reply “Have a damned day.”? After all, if the can push their blessings on me, don’t I have the right to respond in kind?