Sounds more like a nombo to me. When you play Taxman, you cost them $1 on their next turn, but cost yourself $2 this turn compared to buying some terminal silver with your $4 buy. You kind of get a little back from having the Silver next turn, but it's more of a long-term card, useful for when you want to have less Coppers and more Silvers. IGG, on the other hand, is not a long-term card. You want to get them asap, and Taxman doesn't help.