In Numbers 3.0 is there a means to have a dark or heavier line every (5) lines for both the columns across and rows down?
This can be accomplished manually.
Changing cell border line weight
- Select the desired row(s) [Multiple rows can be selected using the ⌘ +Click method.]
- Select Cell tab in the Format inspector pane
- Select the desired border [i.e.: Top, bottom, left, right, all]
- Change the line style and thickness (weight)
Repeat for each desired row. The Copy Style / Paste Style buttons can speed up your work as well.