A Penny's Worth ?

A chap walks up to the counter at the shop with a headtorch, I scan the barcode and the computerised cash register shows £ 7.00.
The transaction followed thus...........
"That's £ 7.00 please sir"
"No it isn't, it's cheaper than that on the tag on the show model"
"Oh, sir, perhaps there has been a mistake"
His manner changed and he stomped the full length of the shop to collect the price tag on display.
 He strolled back with a victorious look, exclaiming "There see, I was right"
I looked at the tag .... £6.99.
"I'm so sorry sir, the computer seems to have rounded it up to £7, of course I will amend the price down, would you like a bag sir ?"
"Yes please"
"That'll be a penny sir," I said, with tongue firmly in cheek.