In a rational stock market (and there are numerous reasons why that might not apply) the value of a share reflects the expected future earnings from holding the share. The expected future earnings come in the form of dividends that the company distributes from the profit they make. So if a retailer’s costs increase, they put prices up to maintain the exact same profit, and sales do not fall, then you would not expect share price to change, because you would not expect any change to the future earnings from holding a share.

Of course, when prices change, it influences sales. But not always in the same way (because goods can be more or less elastic or - less so at supermarkets - luxury goods) and not always predictably; and since the expectation is about predicting behaviour, that means share price doesn’t even necessarily reflect what actually happens.