Currently you can enter Role Rates in Cost Tracker for each team member role. Both Cost Rate and Billing Rate. Seems odd that you can't access this data via any API as it is core data. Either a distinct API where you supply role.id or even included in the Team Membership call as additional attributes.
Tempo Products | Cost Tracker for Tempo Timesheets |
Tempo Platform | Cloud |
This is available and can be found here https://apidocs.tempo.io/cost-tracker/#tag/Global-Rates/operation/setGlobalCostRatesByRoleInBulk