Totals without showing each contact in Contact related reports
one way to do this would be to use the Aggregation feature in Drupal Views. This can be set to give you a 'count' for any of the fields in the row, so you could have your postcode in one column and a 'count' of the 'contact IDs' in the next. You would then be able to make the 'postcode' function as a link so that you could then click through to see all the contacts in that postcode.

Of course it really depends what you want to 'do' with that data after you see it. But if reporting the numbers is the primary goal, this may work for you.

Expect others to provide a 'how to' using Reports directly.