Increase space between promoted links

We are using SharePoint 2013 and one of the things we would like to do is increase the white space between the tiles in the web part. The size of the tiles are fine, we just want to space them out.

There may be several promoted link web parts on a single page, so we would only want to change the spacing on one of them and not all of them. Can/how could we do this?

For example if each D represented a tile within a single promoted links web part, by default it looks like:

D D D D

and we want it to look like:

D     D     D     D

Thanks!