That's simple.
1. Go in System->Taxes, click on "manage tax rate"
2. If you don't have a tax rate, you need to create it.
3. Go in System->Taxes, click on new in order to create a new tax rule
4. Select the zone of the tax (Arkansas), the rate, the default tax category, publish it and save.
5. In your products make sure that the default tax category is selected.
6. Set a "main tax zone" other than Arkansas in the configuration page of HikaShop.
You tax is now setup. After Customers enter their address in your checkout, the tax will be added to the cart automatically.