The Small Package Quotes and LTL Freight Quotes products are real-time rating engines. Provided the shipping parameters used during the checkout process are identical to those used to invoice the shipment, the shipping rate will match to the penny. If they differ there are differences in the shipping parameters.
To reconcile the differences compare the details on your invoice to the settings and shipping parameters recorded in your store. Remember that the weight of packaging materials is included in the billable weight of the package. Consider making changes as needed.
If you are using the Small Package Quotes product and are experiencing differences, make sure that you have dimensions entered for all your products. Dimensional weight can be determining the billable weight of your packages and can cause significant variances in the quoted rate and invoiced charges. Take advantage of the optional Standard Box Sizes feature to achieve maximum rate accuracy.