How bad will my credit report be affected if I open and close a credit card?

When I go shopping, the store asks me if I want to save xx% off my purchase by signing up for a credit card. How bad will it affect my credit score if I sign up to get the discount. Pay it all off right away and canceling right after that? My first credit card received was in 2001 and I never plan on cancelling it.|||If you do it often, it will have a negative effect. What shows is a record of frequently applying for new credit.