Why not use the generic model and allow people to switch to the chips they like
2048 m BTC: change to 2btc
4096 m BTC: change to 4 BTCs
8192 m BTC: change to 8 BTCs
The rationale behind this is actually explained in the FAQ:
And in case you really, really want "round" BTC chips:
Using this action will cost you the weird part of chip which is around 2% fee.
A fee of 2% is well within the range that is customary for mixing services.