Multiple taxes are not yet possible. You will have to have only one tax of 13% (50% of the price with a tax of 7% and 50% of the price), and a price of 26,55 (because 13% of 26.55 will be the difference between 26.55 and 30).
You can always add in the description of the product the tax splitting explanation.
We're working actually on a multi tax system for HikaShop which should be available in next release in January or February.