Please tell what you people do:

I understand that:
1) The 3rd normal form is the ideal way to designing a database.
2) One of the requirements of 3rd normal form is that no fields contain redundant information. This in turn means no field should exist which can be calculated by summing values from a child table.

I find two problems with this:
1) Considerable time is spent summing the same data again and again.
2) There is no easy and efficient way (with SQL) of obtaining a single record for each transaction that shows the total of each summary category. This of course is needed to create effective reports.

Consider our situation: Our transactions can contain 100 different kinds of income, which can be subdivided into ten summary categories on which most reports are based. Is there something inherently wrong with creating a field in the transaction table for each of the summary categories?

What do the purists say? What do you people do in reality?

TIA,

Alex