Regardless, 6.99 is so close to 7, that simply making it 7 is more honest. I'll pay the extra cent for the increased honesty/clarity.

And yes with 1 product it is still relatively easy (provided you put effort) but the more you buy in the grocery store the less oversight you get.

Because generally people will only read whole number and omit the cents, making the price appear lower then it is.

Yes, it is so close to 7 that describing it as 6 is dishonest (we are not talking about 6.50 or 6.51). The brain is lazy and doesn't process it as 7 whereas the relevant part (7) is left out to deceive the customer into buying the product (marketing trick is probably straight out of book of Edward Bernays).

Instead, the product should be good on its own merit; so for me its an orange flag (or rather: proper, informative rounding is a green flag).

We see it elsewhere too. 199 instead of 200. 999 instead of 1000. Etc.

Psychologically dishonest perhaps, which is why it’s so widely used. We seem to give the first part of the number more weight. Same with birthdays. 28 to 29 isn’t a big deal, but 29 turning 30 is a big deal (or any multiple of ten).