Solution : https://service.sap.com/sap/support/notes/316707 (SAP Service marketplace login required)
Key words : 
additional key words rounding, enjoy purchase order, purchase order quantity, attached advance correction, note includes rounding, rounding functions, rounding profiles, rounding values, related notes, material master
Related Notes : 
       
| 301105 | Unwanted rounding to rounding value (ME386) | 
| 300252 | ME21N/ME22N:Repeated rounding after incorrct roundg | 
| 210114 | ME21N/ME22N: implementation of rounding function |