Tax code will not have any relevance in Import Purchase with CIN. You can create a new Zero tax code and make use of it in Import Purchase order if required.
In Import, You will use the Pricing conditions for Excise duty condition types like CVD, Cess, SEcess, BCD, Cess on BCD etc.. You can also use Pricing conditions for Insurance, Handling charges, PF charges and Freight charges if any..
Please go through the below link and you will understand the Import procedure with CIN.