The problem, I think, is that they round off to the nearest even ten. Bloody hell, we would not want this to look like science - people might refuse to read the label. My wife refuses even now.
To illustrate, assuming that the real figure per bar is 56 calories:
1 bar, 56 calories rounded to the nearest 10: 60 calories
2 bars: 2x56=112, rounded to nearest 10: 110 calories
6 bars 6X56=336, rounded to the nearest 10 : 340 calories
There ya have it. Science avoidance at all costs.