Please do not take this the wrong way--Just advice.
Its only a matter of time until you get audited. I knew my day was comming 3-4 years ago. Everyone was being audited, and my cpa confirmed that also. My day arrived and they didnt look at anthing on my tax returns. I locked them out of all things in my quickbook except for invoices and income statements. It took 1 day for them. Plus they had to do the adit at my cpa's.
The state of MN is in a finacial mess as I hear WI is also. According to my CPA the state has hired an additional 50 auditers just for sales tax.
If you are good at the invoice pad thing--great. I know I could never do it because to many items that get taxed and dont get taxed and diffrent taxing area's. I have 6 diffrent sales tax rates to track, collect and break out for the state.
Again, this site is for sharing information. This is my 2cents