Tag Libaries: setting format

I see that Ben M interpreted your question differently than I did.  Tag libraries effect code formatting.  CSS effects content style in Design/Live view.

Edit Tag Libraries (see screenshot).

That's the best you can do.  DW does not automatically insert blank lines between code. 

If you want blank lines, do it manually.

I'm not sure why you are using the tag library for this.  In your CSS if you want all H5's to have margin above and below just do:

h5 { margin: 1.5em auto; }

Just change that 1.5em value to whatever you want your padding to be on the H5 element and you should be all set.