This is unusual particularly with a theme as common as dawn. This could probably be a temporary issue.
I am not sure about this since I am more of a developer than someone who is good setting up these manual stuffs but might be that taxes are getting included in the price if you are charging tax from customers. Please check that from the backend or from the customizer.
If the issue still persist this could be due to a bug in the code which is as I told you unusual, this will need looking up at code in the theme code editor.
Please reach out via mail for a convenient conversation and solution.
Thanks
Shadab Ali