The largest publicly run health plan in the nation, L.A. Care, will let customers pay their health insurance premiums with cash at some 680 locations, including 7-Eleven and Family Dollar stores. At the register, customers scan a bar code sent to their smartphone, then pay cash. The payment posts to L.A. Care within 24 hours, and the service is free to customers. "It's as quick as buying a Slurpee," said Danny Shader, the founder and CEO of PayNearMe, the for-profit company that established the electronic cash transaction network.