There is no statewide law (or federal/national law, for that matter) requiring that gas stations have public restrooms. It is possible that your locality may have ordinances (local laws) requring it: check the town, city, or county code for your areas to see they require it, but if they do not, you don't have to have public restrooms. You can usually find these codes on line; if not, a call to the local building and/or health department can generally answer a question like this.