You must use CISCO-PROCESS-MIB and its object `cpmCPUTotal5minRev` from the table called `cpmCPUTotalTable`, and indexed with `cpmCPUTotalPhysicalIndex`.
The table `cpmCPUTotalTable` allows CISCO-PROCESS-MIB to keep the CPU statistics for different physical entities in the router, such as different CPU chips, a group of CPUs, or CPUs in different modules/cards.
In the case of a single CPU, the `cpmCPUTotalTable` has only one entry.