gst rate change

When you sale the item. you have to charge GST in sales invoice @ 12% and collect 12% from the buyer and pay to govt.

Your purchase will be @ 5% will not matter to sales GST rate that you have to paid to the vendor, as after process raw material get converted into finish good its HSN get change and rate will be change according to GST.

In case of jobwork , as it seems you are sending goods to jobworker and jobworker after processing on goods ,giving back the goods to you only, hence when you send the goods to jobworker you will not charge the GST you will send goods on delivery challan and the jobworker will charge you only service charges of his process and return the goods to you.

For this process you have to file ITC 04 GST return.