Hi!

I'm new to Inkscape. I'm trying to create a logo. I want to use many "fake cubes" to build a large part of the logo. I just couldn't get the built-in cube object to look right, so I tried making one myself. I quickly found a youtube video showing me how to make such "fake cubes" out of 3 squares, and reused many copies of the same one, just with different colors.

Now my problem is that when I look at the whole logo, such that I can see it completely, I can see small "cracks/gaps" between the faces of those cubes, around the one corner that is shared by all 3 squares, which also shows in the bitmap rendering, but if I just copy a single one, paste it somewhere on it's own, and zoom on it until it takes the whole screen, so that I can work precisely, it does not show any such crack/gap anymore, so I don't know how to get rid of them. Could it be some kind of mathematical "rounding issue"?

It's a bug, already reported. It has something to do with anti-aliasing.

There are 2 workarounds. One is to just extend the edges where they meet to where they slightly overlap each other (or rather, "underlap"). The other is a relatively new filter, called Stitch, written just for this problem. You can find a link in this topic: viewtopic.php?f=5&t=9034&p=33279&hilit=stitch#p32882

You might want to read this topic -it is quite short - and see if the workaround there helps.
http://www.inkscapeforum.com/viewtopic.php?f=29&t=9866&hilit=+resolution