Normally workflows run for items so approval of 100 items would mean 100 separate workflows and 100 notifications/tasks for the approval process. This is not very SharePoint friendly as workflows will be run with delay as SharePoint will not start them all at once.
However you could have a site workflow that queries items from your approval list like "all not approved items from department X" and show them in a mail or with a bit of efford in a form. Once the user approves the single task naming all the items the workflow will continue and set some custom status column from "not approved" to "approved".
Would that be working for you?
Best regards
Enrico
so does it mean you have a set of items (eg.) per department and you want to approve all of them at once or reject all of them at once by the same (group of) approver(s)?
if so, then I wouldn't focus on single items at all.
I would create some master object/item like 'Request per IT' and let the workflow run on that master object.
you could link single items to the master object through lookup field and then use this field to identify which items are being (or afterwards were) approved within that master request.