Happy Turkey Day from the US of A . <| sep |> You ' d be surprised . Sales tax in America is very weird . Cities have their own sales tax . The borders of cities change . Parts of cities have special sales taxes . The borders of those parts change . Some items are taxed , some aren ' t , some are taxed at different rates . Oh , big city just added a big soda tax . Google could pull it off , a dedicated company could pull it off , a large corporation would consider it not worth the effort and do things the way they are now . I worked on a project for a company that wanted to do this for their sales . We figured out that it would take more work to keep up the system and implement the flexibility needed than it was currently costing to do it by hand .