When uploading receipts can you do one bulk upload under the expense report vs doing individual receipts under transaction?

Yes, you can by enabling the "Receipt" field on the report header level by going to Masters-> Report Type Mapping when logged in as Admin.

Then select the report type on which you would like to add a receipt field and click on "Header Details" button.

Enable Receipt field - you can then make it mandatory as well. Your system admin will have to do this for you. 

However, even if you do enable the field, you can attach only one file on the report header. It could be a multi-page PDF, but there is only one file you could attach.