For those of you with the 3% JCB Marukai, you can pay your federal taxes with this card and make out ahead of the fees:
https://www.officialpayments.com/fed/index.jspThey charge 2.35% so you net 0.75% on federal tax payments, plus you can get the float on the money until the bill comes due. Further, I've found that if your credit limit is too low, you can pay down the account to a negative balance and you can charge up to your credit limit, so if your limit was $2,500 and you paid the account down to negative $2,500, you could make a single $5,000 charge and have it go through.
For those