The problem is not income taxes, but sales taxes.
You should be registered to collect and remit sales taxes before opening for business, either online or off.
Legally, if you collect sales taxes without being registered, you are stealing. And if you sell without sales tax then you are personally responsible for them.
Most states you can now register online for a sales tax account in just a matter of minutes. Not a big deal and you can be legal the same day.
Here's a link to a site with more info and a link to the NJ sales tax site -
Small Business FAQs