Commission table is available in the Account manager and in Automatic Analysis -> Settings window, "General" tab, "Commission and rates: Define..."
In this window you can enter commission taken by buy/sell transactions.
There are 5 tiers of commission schedule table plus "default" tier that is used when others are not defined or transaction does not match any tier defined. Tiers can be defined based on transaction value or number of shares/contracts traded. Each tier has user definable minimum and maximum. If min/max is not defined or set to zero - the tier is not active.
Each tier allows to define commission on per-share, per-trade, % of trade volume basis and allows to define minimum and maximum commission values based on dollar or percent values.