Round up- two bob, 3 bob, 6 bob. That's eleven shillings. Now take off the odd bits

Even in these decimal days people don't seem to get that trick. Back in more affluent times I bought three CDs at a festival. They were two at £12.99 and one at £13.99. I watched in amazement as the chap wrote them in a column and went 9+9+9 is 27, write down the 7 and carry 2...