Reports and Roll up fields

Hi Guys,

I'm new to MS CRM and facing some issues it would be really great to get any help.

My 1st question is:

Who to display opportunity stage categories on report?

2nd question is

I have a roll up(Sum) field on opportunity which is related to opportunity line item and the sum is not calculated correctly.

Ex - Actual Sum should be 1000.00

      Calculated sum I'm getting is 1000.11

Thanks.