How can i check for Role when calculating an incentive based on role wise rate table.

Hi,

Anyone can help me to configure a scenario which is based on role. a rate table having 3 roles  A,B and C and all having different rates. when i enter a transaction how can we check for a particular role? Is there any standard solution without custom function?or if any custom function needed kindly let share the sample custom Function.

Thanks,

Samina