I'm sure someone will be able to advise better, but I think a good place to start would be to check the websites of some of the major retailers that you are interested in working for. I suspect many will have centrally-coordinated recruitment processes rather than done by individual stores. It will vary from place to place, and the best thing you can do is research what each place wants so you're doing it right for them.

I just wanted to say, that you've already got both sales and customer-service experience (newsagent and travel) so emphasise the transferable skills that those positions gave you by setting your resume out in a skills-based format. Include every aspect of those skills, eg (just going off the top of my head) sales, customer service, stock-taking, competent/confident with cash registers/inventory searching, etc etc. Emphasis your wins, eg if your sales record was particularly good or you got any compliments from employers or customers.