Can you tell me which states you're seeing sales taxes applied to when orders are placed? Are you based solely out of Iowa, and have no nexus in any other US state?
If you head to Settings > Taxes, you should see that you are collecting taxes for the USA. If you press "Edit" here, you should then be taken to a page that shows the physical presences you have listed in Shopify. The system will use this information to dictate when to charge taxes in the US, based on the customer's location. Please let me know what you see here.
Victor | Shopify Social Care