It is possible to add salary rules directly to a task, to accommodate salary or bonuses payed for working on certain tasks.
Adding a salary rule to a task.
When the salary module is enabled, a new tab "salary" becomes available on each task.
From here you can create a new rule.
The rule is created like a normal salary rule, except that it is applied to all the hours that a user works on the task. Also an additional field is available, where one can select if this rule should apply to every salary model, or just a selected few.