I do that mentally as well, but I generally ignore the word “sale”, and just focus on the most frequent low price.

Around a decade ago I regularly bought a particular food product for $10.99. Then one week it was 13.99. The following week it was “on sale” for 11.99. Then it went up to 12.99 for a few weeks before going back to 10.99. It was eye opening and I also learned to stock certain products.