Creating iTunes ID using existing Apple ID
When you registered at developer.apple.com, had you Provided credit card information? If you had, the card information which iTunes needed must same as it. Don't worry，if you don't purchase anything, it will not incur any costs.
Actually, you can register an Apple ID without credit card. Go to the App Store, pick a free app to download. And click Creat Apple ID. Now you can Select NONE when it asks you credit card details.