No offence man but what happens when you need a different shape.
1: open photoshop
2: create a new psd
3: click and hold the square tool (different tools will pop open)
4: select rounded rectangle tool
5: click and drag on the white area to draw your rounded square
6: make sure the square layer is selected and click on opacity
(its in the layers box at the top right side) then change the transparency to whatever you like.
7: do a happy dance
8: see the radius option above the canvas? The bigger the radius the larger the corners.