Hi, Jim,
Go into Format > Paragraph and set the line spacing to Exactly, and type in
14.2 pt (because there are 72 points per inch and 72/5 = 14.2).
You could do this for all your new documents by making this change in
Normal.dot, but I don't recommend it. Make a new template, set the spacing
there, and use that template to base new documents where you want the
spacing. Most documents should remain at Auto spacing. (For one thing, if
you use supercripts or larger fonts, the Exactly setting will cut them off.)