Set the rounding on the BOM line to be whole numbers. The system is back calculating probably for scrap percentages, and from your earlier posts I would guess there has been some development work that is causing you these issues. http://dynamicsuser.net/forums/t/39420.aspx
On the rounding up method and the setting quantity and the multiple to be 1 on the BOM line. This is masking a differnet issue you clearly have with your database that it has some rogue code in it relating to BOMs and production orders, if I was you I would sort that out and not try to work around it.