Hi,
Prices indeed only support 5 decimals by default.
To change that, you'll have to edit the table hikashop_price via your PHPMyAdmin and edit the options of the "price_value" column to change the number of decimals:
www.tutorialspoint.com/how-to-specify-de...ase-using-phpmyadmin
Also, note that in the settings of your currency, you can configure the number of decimals which will be applied when displaying prices in that currency. So I also recommend you to check the number of decimals setting of your currency in the menu System>Currencies.