They provide a variety of services, from helping you pick out items to ringing up your purchases. Like cashiers, retail sales associates use cash registers to process transactions and are responsible for keeping track of all the money inside.
You can refer book for Retail Sales Associate.
Book Name-Sales Associate SYLLABUS/ CURRICULUM
Softcopy available in NSDC site.
Link : http://www.nsdcindia.org/sites/default/files/files/Curriculm-SalesAssociate.pdf