Ok, let's do the maths shall we?
Tesco's annual profits most recently were £3.13bn. Sounds like an awful lot of money doesn't it. https://news.sky.com/story/profits-up-at-tesco-after-job-cuts-with-further-losses-not-ruled-out-13345570
Per day, that is £3,130,000,000 / 365 = £8,575,342.
Google tells me Tesco has 2,973 stores in the UK as of July.
£8,575,342 / 2,973 = £2,884 profit per store per day.
£2,884 profit per day, over let's say an average of 1,000 customers per day (I personally think that's too low but we'll go with it) = £2.84 profit per customer.
Let's say customers buy on average 20 items, that's 14p profit per item.
And this does NOT include profits from petrol, phone plans, insurance, and all the other services they provide.
The average profit element on any item you buy in store is literal pennies. If Tesco decided to make no profit at all, the difference in your weekly shop would be £5-£10 at most.
They make so much profit because they turn over unimaginably huge volumes of stock, not because they're price gouging.