1. A system for classifying a new item for purposes of estimating an import fee associated with the new item, the system comprising: a data store that stores information regarding a plurality of previously classified items, the information regarding each previously classified item comprising a classification code that may be used to estimate an import fee associated with each previously classified item; and a computing system comprising one or more computing devices, said computing system in communication with the data store and operative to: for each of a plurality of previously classified items, calculate an item similarity score representing a relative level of similarity between a given previously classified item and the new item, wherein the item similarity score for the given previously classified item is calculated at least partly by: determining an attribute similarity score for the given previously classified item, wherein the attribute similarity score is determined at least in part by determining a number of common attributes associated with the given previously classified item and the new item, wherein a common attribute comprises an attribute that is associated with the given previously classified item and is also associated with the new item; and determining an attribute value similarity score for the given previously classified item, wherein the attribute value similarity score is determined at least in part by determining a number of attribute values, of one or more of the common attributes, that are associated with an attribute of the given previously classified item and also associated with a corresponding attribute of the new item; wherein the item similarity score is calculated based at least in part on both the determined attribute similarity score and the determined attribute value similarity score; and determine a closest item match for the new item, wherein the closest item match corresponds to a previously classified item having a highest degree of similarity to the new item among the plurality of previously classified items based on item similarity score; assign an item classification code associated with the closest item match to the new item for purposes of estimating an import fee associated with the new item; and estimate an import fee associated with the new item based on the assigned item classification code.