You only need to collect taxes on your online sales to shipments in Missouri. Since you will be charging online customers sales tax your sales to Missouri residents will probably be pretty low. Most online customers don't like paying sales tax. We are located in Massachusetts, but sales within our state only account for 3 percent of sales. We use an order fulfillment system that keeps track of sales tax collected. We then send this amount to the state monthly.  

I assume your tradeshows are all over the country.  Each state has different rules regarding Nexus.  If it is determined that you have nexus in certain states, you might consider hiring a professional firm to file your sales tax returns in preparation for a tax audit.

Usually in US when you are selling a product you have to charge sales tax. When you provide a service then in some states there is no sales tax. The trick with charging sales taxes is that you will have to account them too when you are making you tax refunds. That will just take you a lot more time so I suggest you do them every 4 months. Regards

In MO make sure you check local sales taxes. You can find the info on http://dor.mo.gov

Melanie, Congratulations on starting a new business. Take a look at Starting an Online Business. You do have to follow local/state/federal laws when it comes to taxing. Since each state is different, I would suggest calling the MO Department of Revenue. Take a look at our business article about How to Legally Sell at Flea Markets, Shows, etc. You do have to collect sales tax at those shows. Here is a direct link to MO Department of Revenue for selling as Special Events. I hope this helps and good luck. JimD