The disclosed system and methods adjust one or more parameters affecting the purchase of one or more items and change a buyer interface in order to display the consolidated parameter to a buyer. Example embodiments include a machine-implemented method for detecting an edit to the shopping cart, conducting a complex parameter editing simulation based on data accessed from multiple databases, adjusting a parameter associated with an item in the shopping cart, and adjusting and displaying a cart total to the buyer. The system can further receive an indication to checkout the shopping cart and edit complex parameters during checkout accordingly.