Auditing managers is important. Most managers can put 1 and 1 together and figure out how to hit you hard. Look for checkouts deleted, checks reopened and items voided.
For employees look to voids, no-sales, open items as mentioned by bigblok. Also look at comps and promos. Be sure to spot check the the times and dates of voids, comps etc and compare to your manager's schedule. Surprising how many comps and voids can show up on a manager's number when they are not working if you do not have a policy of passwords and mag cards for managers.