Since I upgraded to 6.3.2, I use XML Tools
.
- install XML Tools via the Plugin Admin (Plugins ? Plugins Admin... Then search for "XML Tools", check its box and click the "Install" button).
- use the shortcut Ctrl+Alt+Shift+B (or
menu ? Plugins ? XML Tools ? Pretty Print)


In older versions:
menu ? TextFX ? HTML Tidy ? Tidy: Reindent XML.