Collecting taxes – Some customers are tax exempt – How do you not collect taxes

At least half of my customers are tax exempt – either non profits or using the products for resale to others. A feature WPeC needs is to have a way to exempt a non profit from having taxes collected at checkout. Now I have taxes set at 8% across the US. But that causes as many customer issues as it solves. How do others deal with the people who claim “tax exempt”? I ask them to fax or email their exemption paperwork. I’m in the US and each state is different, and then manually send them an invoice for what they want to order. I’m hoping for some of checkbox perhaps, that would say “I’m tax exempt” and then have them be instructed to send in their paperwork – of course, everyone will say they are tax exempt, but hopefully I can have the sale compelated and sort out the paperwork later as opposed to someone leaving the site without completing the sale- which is what is happening now. How do others deal with this issue? Some states don’t collects sales tax either, others are higher than 8%, I know it’s a problem and collecting taxes is going to be the site owner’s responsibility soon if it isn’t already. Looking guidance on how to approach this. Thank you.