Yes, it is possible within Toodledo itself. Here are the necessary steps:
Go to "Tools" (in center on top), then "Import/Export/Backup", then into "CSV Import/Export" by clicking on "More Details..." under it. Under "CSV Tasks Export" next to "Completed Tasks:", click "Download CSV file" and save it to your desired location. Open the CSV file using a spreadsheet editor (e.g., Excel) and sort accordingly.