I also recommend a scheme such as moffy recommend except I suggest having the bottom resistors switched in parallel. R1 is fixed. R2 would be unswitched. R3 is in parallel with R2 and switched by a SPST relay (S1). R4 is in parallel with R2 also and switched by a second SPST relay (S2). With both relays open adjust R2 to give 9.5V. Close S1 and adjust R3 to give 8.0V. Close S1 and S2 and adjust R4 to give 5.5V.
With those connections the voltage will be 9.5V with both relays open, 8.0V with S1 closed, and 5.5V with both S1 and S2 closed, and it will change between levels with only two SPST relays.