Actually in CA, many groceries are not subject to sales tax, just FYI. I'm not sure where the distinction is drawn, but it seems like the less processed the food the less likely it will be taxed.
The original idea was to reduce the regressive effects of sales tax by making basic necessities tax free. Coffee, ground beef, and potatoes are considered basic, but having someone prepare your food for you is a luxury. This general philosophy based on need has been around for decades (centuries?), and it was not originally motivated by getting to people to "eat less processed foods" or other health reasons. Of course, since then all sorts of changes have been made for a variety of reasons.
Not sure why this is downvoted. California, like many other jurisdictions, seems to make a distinction between groceries/"raw" foods, and "prepared foods" when it comes to sales taxes. Unprepared foods are generally exempt from sales tax, while store-prepared foods are not exempt. E.g. an unsliced bagel in NY is untaxed, but a sliced bagel can/must be taxed. Fruit and vegetables likely fall into the untaxed category.
From Wikipedia: In grocery stores, unprepared food items are not taxed but vitamins and all other items are. Ready-to-eat hot foods, whether sold by supermarkets or other vendors, are taxed. Restaurant bills are taxed. As an exception, hot beverages and bakery items are tax-exempt if and only if they are for take-out and are not sold with any other hot food. If consumed on the seller's premises, such items are taxed like restaurant meals. All other food is exempt from sales tax.
It is more complex that that: hot food might not be taxed if it is "to go" (Starbucks and their breakfast sandwiches ....), Whole Foods will always apply tax to its food bar items, the ice cream parlor down the street will apply sales tax if you say "for here" but not if they assume take out.
It is very very confusing, and I haven't really figured it out yet.
Sales tax on food in general tend to be pretty arcane. Notoriously, McVities sued the British revenue services to have some of their biscuits classified as cake instead of biscuits, because there's no VAT on cake. (They won.)
Actually in CA, many groceries are not subject to sales tax, just FYI. I'm not sure where the distinction is drawn, but it seems like the less processed the food the less likely it will be taxed.