Well, I usually design ships with standardized sizes (2000/4000/8000/12000t etc) so I definitely wouldn't need this, but I suppose that most players do the same, so you won't find ships with minimal size differences (if one of my ship designs ends up with 12050t, and I know my jump tender supports 12000, I'll rework it so it falls under 12000).
Changing this would be quite an unnecessary complication.