Goods transported by A from delhi to B mumbai. 
Transport charges paid by B on receipt of goods in mumbai.
GST ₹56 mentioned on the cash receipt issued to B (on amount of ₹1120) to be paid by B

In this case GST ₹56 will be recorded as IGST ₹56 or SGST and CGST ₹28 each

Please let me know and what's the rationale for the same. Thank you