Do we need to install Update Rollups 1 through to 5 in order?
The answer is no. Exchange Update Rollups are cumulative. Cumulative means it contains all previous hotfixes. Exchange 2010 Update Rollup 5 also contains update rollups 1-4.
You only need to install the latest service pack followed by the latest update rollup.
For a list of update rollups and build numbers please see the following link: