As for the fixed tax, it doesn't apply to you. Fixed tax refers to mobile vendors, vegetable markets, aquatic products and other industries. If you charge a fixed tax, you must not know whose pocket the ashes are.
I suggest that you don't be greedy and do bad things. Since opening a store, I definitely want to develop for a long time. You must legalize yourself first. It is the best choice to go through all the necessary procedures and protect yourself by law.