Hey there Natalie!
Justin here from the Shopify Support Team! Thanks for reaching out to us today!
There is actually a Donations App available on our App Store, it is called 'Share the Love' and you can find it here: https://apps.shopify.com/share-the-love
If that doesn't work for your store you could always add the Donation as few products, in different denominations and create it on a Page/Collection and then use this App, so that your customers can receive tax receipts: https://apps.shopify.com/tax-receipts
Let me know if you have any other questions at all !
Justin | Shopify Support Guru
I don't know if you're still looking but we've developed an extension that sounds exactly like what you're looking for and is really easy to integrate and set up.
It also works as a solution to increase customer conversion and retention and is a fun way for your shoppers to interact with your brand.
Have a look and let us know what you think.
All the best
I'm one of the developers working on TipGenius, a simple tipping or donation pop-up app for your Shopify store checkout. We're the Staff Pick this week!
When a customer clicks the checkout button, TipGenius shows a customizable pop-up that let's you ask for a tip or a donation, and then sends the customer right through to payment. It's simple to setup and simple for customers to use. I think it could really help here.
Check us out at https://apps.shopify.com/tipgenius
Your wish has arrived! Shopify just announced integrated "tipping" which works just as well for donations! (Just need to edit the languages section of your theme - see bottom of following linked page.)
I just added to essentialsupply.us and looks great (though I have not seen where to default the checkbox for tips to "off.")
To relabel things so it makes more since to customers, most of the translation keys are under checkout & system in your themes language editor
Be sure to also update your notification email templates and do some test orders.
Here's a demo store experimenting with using tips as surcharges on the payment screen during checkout https://tipsasfees.myshopify.com/