This could be due to the country set for your account is incorrect. To check this please follow the instructions below;
1. Log into your account at https://store.harrisonaudio.com/login?back=my-account
2. Click on Addresses
3. Select Create new address
4. Fill out the details Ensuring that your Country is set.
5.Go back to your cart and clear any products out, Then put in the product that you are looking for. The Tax should no longer be on there.