I've been using this tutorial, but can't seem to get it to work. I can get the box in there, but it won't add the tip to the total.
My team and I recently created TipGenius, a simple tipping pop-up app for your Shopify store checkout; we are the Staff Pick this week!
With TipGenius, when a customer clicks your checkout button, a pop-up window gently asks if they would like to add a tip.
Check it out at https://apps.shopify.com/tipgenius
You have multiple solutions now:
A) Shopify just released a feature to allow tips at checkout: https://help.shopify.com/en/manual/checkout-settings/tips
Go to Settings > Checkout to enable and enter your tip amounts.
Here's what it looks like:
B) If you need it anywhere else, Tip Jar lets you add a customizable tip widget (or donations, or gift wrap, or add-on) anywhere in your theme.
My team and I built Tip Jar, and we love feature requests so if you need anything custom just hit us up. We're a team of experienced Shopify developers that enjoy helping Shopify stores be more successful.