hi sir,
I am magento developer with 1- yrs php experience.
This can be done by adding new attribute to product, call COD, and options are true / false
Then i can programming it in magento local script to detect if the items has COD or not.
The NaN% issue also can be fixed.
Feel free to check out my profile. Some highlights regarding magento are:
https://www.freelancer.com/projects/Magento-Newsletter-Subscription-Popup.4050463.html
https://www.freelancer.com/projects/PHP-Excel/Spreadsheet-sync-with-Magento.html
https://www.freelancer.com/projects/1300613.html
https://www.freelancer.com/projects/PHP-Javascript/Magento-Developer.1222440.html
https://www.freelancer.com/projects/PHP-Data-Processing/Modify-Order-Data-Magento-Database.html
Looking forward to hear from you!
Regards,
phpSQLexpert