This is a two-part request
1) Create Donation page on which the user has the option to add an amount of their own choosing. Page should also include pre-determined amounts
2) Add Donation feature on the order confirmation page to ask the user if they would like to donate money to the organization (allowing them to enter in any amount). Donation feature should NOT ask them if they already have a Donation in their cart (that is, they are already giving money by using the page created in part 1). Plus if they choose to donate from the confirmation page, it should NOT redirect them back to their shopping cart, but rather simply refresh the order confirmation page with the donation item added with the amount they entered to donate.
Donations should not be taxed.
Note: Current store is already highly customized