A discrepancy of a few dollars isn't going to raise any eyebrows at the IRS. As you mentioned, this is likely due to rounding and won't make a material difference on your tax return, if any.
Yes, you should enter the cumulative amounts of income and deductions for each of the periods presented on the 2210. For other taxes, you can allocate to each period based on the percentage of income being reported in each period.
