How to create groups with ireport

How to create groups with ireport

I have a dataset like below
order_no date tot
1 2013/08/21 5500
2 2013/08/22 12500
3 2013/08/23 8000
4 2013/08/24 27000
5 2013/08/25 18000
I want to create groups in a report in ireport which the last
column("tot") values are grouped into ranges as below 5000,below 15000,
below 25000 and over 25000.I want to know how to write the group
expression.
the report should look like this
Below 5000
order_no date tot
1 2013/08/21 5500
Below 15000
order_no date tot
2 2013/08/22 12500
3 2013/08/23 8000
Below 25000
order_no date tot
5 2013/08/25 18000
Over 25000
order_no date tot
4 2013/08/24 27000
plzzzzz help me.