I've never tried this, but I guess this will work (sorry to say, but still with iTunes involved)
1. Transfer alert tones from iPhone 5s to your PC
Connect your iPhone 5s to your PC
iTunes will launch automatically (if don't, do it yourself)
Transfer purchased alert tones from "iPhone" > "Purchased" to your PC (this screenshot is of my iPad 4, but I guess they're all the same)
BTW, If the iTunes Store purchases on your device were purchased with multiple accounts, you will need to authorize the computer for each one. here's a support article from Apple
iTunes Store: Transferring purchases from your iOS device or iPod to a computer
2. Transfer alert tones from your PC to your iPad Mini with Retina display
Connect your iPad to your PC and click "Tones", make sure to tick Sync Tones, then choose Apply (again this screenshot is of my iPad 4, but I guess they're all the same)