Hi,
A couple of things to check here
1) When using a tax jur to see the tax rate in a tax engine, it will display 3 rates: sales tax, sellers use tax and consumer use tax. So while posting in SAP check what tax is applicable.
2) While posting in SAP there might be additional taxability drivers or tax rules which are getting triggered and modifying the tax rate.
Please check on the above two.
Regards,
Soumik