Jesse from the Guru Team here.
I would first suggest doing a CSV export to edit your product prices in bulk. You will be able to reimport and overwrite your existing matching products and that will take care of adjusting the prices.
You will also want to review your Tax settings as well to confirm whether or not you have your shop setup to include taxes in your product prices.
https://docs.shopify.com/manual/configuration/store-customization/page-specific/product-page/show-va... (this guide will only work for you if your products have only one variant)
Feel free to reach out at any time if you have any other questions.