Why don't Shopify's collected taxes match our retail store's sales?

We are a pretty simple retail store that sells some food and general merchandise. In so doing, we have our county tax set at 2.25%, our state at 4.75% and some food at 2%. The question is, the taxes collected by Shopify don’t add up. Lets say we have a total of $20000 in total sales, shopify might show $16k in county tax sales and then $15000 in state tax. This isn’t a setting and reports out of Shopify are pretty non-existent. Any help you can provide would be greatly appreciated.