I think what may have burnt me is the CASA rounding/accuracy limits. A lot of my answers/working (EMZWs, max allowable altitude etc.) were very close to the limits/mid points so I worked them accurately (Instead of rounding weights to the nearest 1000KG, temps to nearest 5 degrees etc.).
If the syllabus calls for rounding then that is what you do. If you follow directions, you will find your answers will be almost spot on.