Yellowknife was chosen as a destination because it represents a different type of rock terrain from the one on which Curiosity landed in August and on which it has done most of its driving.
The amount of tax charged on your order will depend upon many factors including Identity of the seller, type of item purchased, and destination of the shipment.
In the episode, titled "Dangers on a Train, " Marge mistakes an Ashley Madison-type website for a Dolly Madison-type cupcake site, not realizing that it's a destination for married people to arrange affairs.