If this is UK site? As I see zen on my test site when adding gear to the checkout it calculates vat as a total ie:

1- £28.49 = vat £4.99
2- £29.99 = vat £5.24
Total inc vat = £68.72
Vat payable = £10.23

so i would suspect you zone rates are wrong in admin. check your zone rates are active, and are at 17.5 not 7% florida default rate.