Yes you can. There are many instances and times a task will need to be cancelled. The ability to cancel a task, and the options for cancelling a task, depend on the status of the task in question. Below you will find the options you have under certain statuses for tasks.
Awarded Tasks which have not been started - If you have awarded a task to a prospective employee and they have not started it you can click the gear icon and cancel the awarded task. This will move the employee back to Application Pending status.
Contract Started by Employee/Contract Working Clock Running - The employer can offer a Mutual Cancellation. The employee can then either mark the task complete, or accept the mutual cancellation with no affect on either the employer's or the employee's score.
Contract Working With Clock Expired - The Employer can pay, offer a Mutual Cancellation (after 48 hours the contract cancels in the employer's favor), offer a 2nd Chance (must be accepted by the employee), or send a cancellation notice which provides the employee with 48 hours to complete the task.
Task Marked Complete by Employee - The employer can pay, not pay, offer a Mutual Cancellation, offer a 2nd Chance (there is now no time limit for acceptance of the 2nd Chance by the employee), offer partial payment, or a full cancellation. An employee can offer a Mutual Cancellation, request a partial payment, request a 2nd Chance, or also submit a full cancellation (Employee must wait 48 hours before a full cancellation option is available, then the employer has 48 hours to make a counter offer to either pay, not pay, Mutual Cancellation, or a 2nd Chance).