I too always round up and then trim after pressing. I have Omnigrid and they all have 1/8" dashes, not a continuous line. Some quilters use the Omnigrid 0.25'' x 21 Yds Glow Line Tape to mark particular lines. Can be found on JAF online:
http://www.joann.com/omnigrid-glow-l...6-62ecee851aad