How to compute it?

Mr. John Smith's attention has been caught by a big neon sign on the supermarket. It was a rather strange sign: it just said "7.11" Puzzled, Mr. Smith entered the shop and found himself in a big hall.

- What's it about? - he asked, rather senselessly, the vendor who came up to greet him.

- Oh, it's simple. We are open from 7 a.m. till 11 p.m. - answered the good man.

Indeed, simple it was. Mr. Smith knew what he wanted to know, so in fact he could leave the place. But, well, once you are in... He chose four products from the colourful shelves and almost immediately he heard the voice of the cashier.

- You pay 7.11.

- What? Why? - he asked, quite surprised.

- It's 7 dollars and 11 cents for all the goods you have chosen, Sir - the answer was very precise.

- Because of the opening hours? - John's surprise was growing.

- No, Sir. I have just taken note of the prices of the goods, then I have multiplied them and the result is 7.11. - explained the cashier.

- You have what?! You should have added them, not multiplied! - Indeed, Sir, I must apologize - the cashier's fingers danced again over the keyboard of a small computer - you pay 7.11.

- You must be joking! - shouted John with irritation.

- No, Sir, please check it yourself.

After a thorough verification John had to admit that the cashier or rather - his computer - has made no mistake in either calculation.

What were the prices of the goods acquired by Mr. Smith? That is our question: How can this be computed?