1. A computerized method to calculate charges relating to a plurality of transactions, the method including: identifying by a payment server, a plurality of transactions that satisfy combinable criteria, the payment server including processing logic; storing one or more item records in a database, the one or more item records representing items available in an online marketplace and each item record having a combinability field indicating whether or not an item is combinable with another item; presenting a plurality of transactions relating to the one or more items to a first party, the first party being a seller of items in the online marketplace; displaying, on a display device communicatively coupled to the payment server, a combinability indicator to the first party, the combinability indicator indicating a subset of the plurality of transactions as combinable; receiving data indicating approval from a first party to combine a subset of the plurality of transactions into a single invoice, the subset of the plurality of transactions identified as being combinable based on the combinability fields of the subset of transactions combined; identifying a rule, specified by the first party, for an automated calculation of charges in connection with invoices issued by the first party, the rule specifying an automated calculation of at least one of a shipping charge, a handling charge, or a shipping insurance charge; and dynamically invoking the rule to calculate a charge for the subset of the plurality of transactions combined in the single invoice to be issued by the first party.