Official comment
Calories and kilojoules are fields that are directly linked in the ingredient and recipe. If you enter a value for one, Genesis will calculate a value for the other. So as long as you have a value for one, you will have the other automatically.
Rounding rules for EU can be found on page 15 of this document:
http://ec.europa.eu/food/safety/docs/labelling_nutrition-vitamins_minerals-guidance_tolerances_1212_en.pdf