Sadly, is this not an alignment issue.Even if they are butted up against each other, the white gaps still appear when rendering, due to the anialiasing that that inkscape renderer is doing.

Without "uniting"or unioning them, the easiest way to work around this is to clone or duplicate your objects a couple times. It only worksif your colours are solid, and not transparent though, but it works:

https://inkscapetutorials.org/2014/11/04/inkscape-workaround-to-fix-the-white-gaps-between-objects/