rounded_corners.sass

// round corners (base)
= border-radius(!radius = 10px)
  -moz-border-radius= !radius
  -webkit-border-radius= !radius
  border-radius= !radius

// top rounded corners
= border-top-radius(!radius = 10px)
  +border-top-left-radius(!radius)
  +border-top-left-radius(!radius)

= border-top-left-radius(!radius = 10px)
  +border-corner-radius(!radius, "bottom", "left")

= border-top-right-radius(!radius = 10px)
  +border-corner-radius(!radius, "bottom", "right")

// bottom rounded corners
= border-bottom-radius(!radius = 10px)
  +border-bottom-left-radius(!radius)
  +border-bottom-right-radius(!radius)  

= border-bottom-left-radius(!radius = 10px)
  +border-corner-radius(!radius, "bottom", "left")

= border-bottom-right-radius(!radius = 10px)
  +border-corner-radius(!radius, "bottom", "right")

= border-corner-radius(!radius, !vertical_position, !horizontal_position)
  :-moz-border-radius-#{!vertical_position}#{!horizontal_position}= !radius
  :-webkit-border-#{!vertical_position}-#{!horizontal_position}-radius= !radius
  :border-#{!vertical_position}-#{!horizontal_position}-radius= !radius

rounded_usage.sass

@import rounded_corners.sass

div.rounded
  +border-radius

div.rounded-top
  +border-top-radius

div.rounded-bottom
  +border-bottom-radius

div.rounded-bottom-left
  +border-bottom-left-radius

div.rounded-bottom-right
  +border-bottom-right-radius

div.rounded-top-left
  +border-top-left-radius

div.rounded-top-right
  +border-top-right-radius