This picture shows the relation between 0.01 cut lines in your software and what remains after cutting the pieces by laser cutter. You can measure tabs and slots width and height in your software and check for correctness.
CaseMaker.com is a nice tool to make boxes with, but the settings has to be right.
I have been experimenting with CaseMaker, and how to find the perfect kurf for a 3 mm acrylic box.
This is my findings.