It looks as though the link you shared is using the app Kaching Bundle Quantity Breaks from the Shopify App store. The app allows you to select which products or collections are eligible for volume discount, set your discount by percentage, dollar discount or specific price and much more.
If you're interested in exploring other product bundle apps, you can check out Shopify Bundles which is a free product bundle app. The app allows you to create fixed bundles and multipacks directly from the Shopify admin and there's no coding or customization required. For a variety of product bundle options, check out the apps we have listed in the Shopify App store.
If you have additional questions, feel free to share them here.
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