Cash prices in many places are lower, so places like gas stations do tons of cash business. I highly doubt Exxon is using cash to evade taxes, thus this is a fantastically poor take.
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Then why would they encourage to use cash using lower prices? It’s more costly to handle cash than to pay credit card companies.
Also, countless examples of people digging into the cash register as part of their position perks, or usual management of remote petrol stations. Need to pay protection money? Cash. Need to pay a provider? Cash.
What evidence do you have they are?
I understand your point about handling cash requiring more labor (no self serve, armored trucks, etc) but I'd be surprised if the cash sales were less profitable than credit cards.
You can run the logs from the pumps vs the log book of fuel purchases. Similar for the convenience store. A brand name station is going to have a computerized register, and sales need to match supply for the most part. There will be some mismatch due to theft, but you can't hide enough cash sales for the tax savings to be worthwhile, IMHO.