Its slogan is "every little helps" and shoppers seemed to agree when they queued outside Tesco to withdraw "free" money being dispensed by the store's cash machine.
The ATM at the supermarket branch in Cranford, Hounslow, in west London, began dispensing £20 notes instead of £10 notes due to what Tesco said was an operational error.
An estimated 150 people withdrew up to £5,000 cash before the machine finally jammed, a spokesman said.
Tesco said it would not be asking for the money back from those who profited from the windfall over the two-hour period in which the extra money was dispensed.
The error, last Thursday, occurred when a bundle of £20 notes was mistakenly put into the slot where there should have been a bundle of £10 notes, Tesco said.
The spokesman said: "This was thankfully an extremely rare operational error."