How do I customise a report (transaction report) to open by default collapsed by grouping )grouped by customer) as I only want to see customer totals

I have a custom report I need for government reporting. It's a transaction report grouped by customer. How do I customer it to by default open so that groupings are collapsed - I only need totals per customer not the expanded list of transactions. Or is there a shortcut to collapse all groups once I open the report?