From what I gather, WI has Nexus and you should be collecting sales tax (depending on what you're providing). Do you mind me asking what you sell online?
You're right about nexus, but I sell a non-tangible SaaS product (no hard-ware, no CD download, etc). It's a grey area, but I think I'm okay. I'll verify at some point soon. It's still a side-thing w/ little to no revenue.