Hello,
If the switch has more than one inband interfaces configured, then for the TACACS traffic it uses first default route configured.
For e.g., if you configured:
set interface sc0 5 10.10.10.2/255.255.255.0
set ip route default 10.10.10.1
For any packets sent to subnet other than local, it forwards to 10.10.10.1, with source IP 10.10.10.2
If you want to use a specific IP/gateway address, then configure that default route as primary.
set ip route default 10.10.10.1 primary
Regards,
Yogesh