If estimated taxes for the PTE filing were made in 2021, then enter those payments on the Information Worksheet in Part III.  The payment will then flow to line 13a of the Form 511.

As for the rounding issue, you are able to edit the pass through entity election tax paid for each member on their respective K-1.  Go to each MD K-1, Part D, line 2 and you are able to edit these amounts to equal the total PTE tax shown on the the Sch K Wks, Part D, line 2.