Group By Time Span

I have a database where user events are recorded quite frequently. I'd like to be able to get a count of the 'good' events that happen in each 5 second period. Unfortunately I don't know how to display and group by a time range.

Here is the query I would like to change:
SELECT count(*), clientTime
FROM dbo.V_COMBINED
WHERE (sessionId = '122b') AND (type = N'sys_goodaction') AND (paraName = 'value')
GROUP BY clientTime

It returns records like:
1 |2006-02-16 23:21:05.250
1 |2006-02-16 23:21:05.267
1 |2006-02-16 23:21:06.470

I'd like it to return records like:
5 |2006-02-16 23:21:06 - 23:21:10
3 |2006-02-16 23:21:11 - 23:21:15
4 |2006-02-16 23:21:16 - 23:21:20

Anyone know how I could do this? Is it even possible?

Thanks