I haven't seen any Chase offers yet this year, but if you pay your taxes with your AMEX you can earn MR points and then transfer those 1:1 into OP miles. But, consider this:

If you pay your taxes by AMEX you are going to pay a convenience fee of about 2.5%. In effect, you're paying 2.5c for each point/mile. This is a really high price to pay for miles. In fact, you could just by MR points outright for 2.5 cents each....