Hi,
I am sorry for the late answer.
We tried to reproduce your issue and I also retry to reproduce it at this moment.
I clicked on the button to edit the additional information, I changed the shipping tax price (which was 0 for the test order) to another price (1.0) and I got a positive result, the global tax changed as required.
I also tried in the other way (reducing the shipping tax).
So I can't reproduce your issue in my local website.
Would it be possible to have more details about your order ?
Why do you write that the VAT should be "1.02" and not "1.64" ?
Once again, sorry for the late answer.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.