InterbankFX confirmed that they allow decimal size trades on regular and minis. While using the MetaTrader4 platform you can trade as low as .01 lot sizes. That's a 100 lot size on the mini.
You can use the live chat on their website to confirm this for yourself!
Im wondering if fxdd.com allows this with MT4 as well.
both offer a 2 pip spread on eur/usd. IB= $500 min to open fxdd= $200 to open
EDIT: Personally I trade with OANDA because I use lot sizes as %NAV and the $1 incrament works well for that. but MT4 has some really nice features for backtesting/automation that I am looking into theres just not much of a choice of brokers using that platform.
Good luck with your search, hope this helps!
-Josh