Documentation about rounding differences between requisition approval amount and PO distribution enc

I am looking for some detailed 12.1.3 documentation on how requisition approval amount is calculated vs. purchase order distribution encumbered amount.  A user presented the following scenario:

PO 5401580 Line 1 has Encumbered Amount 82.54 (this is line 3 of req 1001523)

  However Req 1001523 line 3 shows Amount 82.56 (Approval Amount)

PO line 2 is line 2 of req 1001523, which shows encumbered amount of 82.57 (not 82.54, the req approval amount)

Req line 5 (PO line 3) shows approval amount 82.56 (not 82.58, the PO encumbered amount)

Req line 1 (PO line 4) shows approval amount 82.57 (not 82.58)

Req line 4 (PO line 5) shows approval amount 82.56 (not 82.58)

I explained the following, based on something I have read before, but I can't find the document: