Creating different groups on one report

[NLugo]

Hope you can help...

I have a headcount report set up by
Dept.
Division
Tier1
Tier2
Tier3

What I need to do is set up my report to display the data by different grouping depending on the dept.

For example, for dept 1000 I need to group the data by Tier1 and Tier3. Then for dept 2000, I need to group the data by Tier 2 then Tier 1. How can I set up different groups depending on the dept?

Please help!!