1) No, you do not need to do an amendment for .03.
2) For rounding on .01-.49 it rounds down to the lower dollar, for .50-.99 it gets rounded up to the next dollar. Since .03 would not make any difference in your taxes you do not need to amend them.
3) If you needed to amend you should wait until your taxes have been accepted and you have received your refund.
