Before use of this feature, you must first turn on multiple tax rates (from Control Center -> Manage Tax). You should also create new tax, rates that are item-based by checking the "Apply this tax selected items only".
Example 1: Apply Tax to product with id of 1334631
curl -u 5c4fc5805eb643716bbc17dad456a0c6cf2e23fa:X \
-H "Accept: application/xml" \
-H "Content-Type: application/xml" \ "https://account_id.c2.imonggo.com/api/products/1334631.xml"
-X PUT \
-d "<product><tax_list>Tax 1</tax_list></product>"
Example 2: Apply Multiple Tax rates to product with id of 1334631
curl -u 5c4fc5805eb643716bbc17dad456a0c6cf2e23fa:X \
-H "Accept: application/xml" \
-H "Content-Type: application/xml" \ "https://account_id.c2.imonggo.com/api/products/1334631.xml"
-X PUT \
-d "<product><tax_list>Tax 1, Tax 2</tax_list></product>"
Note: "Tax 1" and "Tax 2" are tax names. They must be item-based tax.