That code should work OK. What browser are you testing it in? You also need to make sure the div has some height, or the % values will be meaningless. The current height of 5px makes it pretty hard to place any roundness on the div. 5% of 5px ain't much. (If you give the div a height of, say, 600px, you'll see that the rounding is indeed working.)
You've specified bottom-right twice, so the bottom-left takes the value of the first (basically redundant) shorthand value.