A simple one

If I buy a certain 4 items priced at:
$1.20
$1.25
$1.50
$3.16

To get the total of these figures, it does not matter
if the prices are added together as one would expect or
if the prices are multiplied. The total bill will be the
same: $7.11. What mathematical principle is being
displayed in this problem?

1.20 * 1.25 * 1.50 * 3.16 =
(((3.16 + 50% ) + 25% ) + 20% )=
3.16 + 1.58 + 1.185 + 1.185=
3.16 + 1.58 + 1.18 + 1.19=
3.16 + 1.50 + 1.20 + 1.25

Originally posted by TheMaster37
1.20 * 1.25 * 1.50 * 3.16 =
(((3.16 + 50% ) + 25% ) + 20% )=
3.16 + 1.58 + 1.185 + 1.185=
3.16 + 1.58 + 1.18 + 1.19=
3.16 + 1.50 + 1.20 + 1.25

Ehm...percentage calculation? Dunno, seems to me that it's simply lucky.