We sell services in USD and then we need to convert the value to CAD to calculate commissions. The problem we’re having is that the auto exchange-rate is always around 5 cents over what the bank rate is. Is there a way to add a rule to modify the automatic exchange-rate with a simple rule?
Thanks
You will need to customize standard behaviour by writing another module to get it done.
Feel free to hire service providers https://erpnext.org/erpnext-jobs if you dont know how to do it.
Or go to Home and start reading… 
Maybe share an numeric example to illustrate and confirm this is not a case of say rounding configuration?