By law your employer can only give you $5250 maximum, tax free. If your tuition was less than that, and you employer reimbursed it all; it’s safe to assume it does not need to be reported. You do not even need to enter your 1098-T if you have one. You have nothing to claim.
If you got more than $5250, the amount above $5250 is usually already included in box 1 of your w-2, as income. Since you have essentially paid tax on that part, it is considered your after tax money and that amount can be used to claim the tuition credit.If you have no out of pocket costs, you cannot claim the education credits. If, for some reason, you left your job and were required to return pay to your employer, then you could claim the credit at that point. Anything that you're not on the hook for (i.e. scholarships, grants, employer reimbursement) cannot be used towards qualifying funds for the education credits.
The amount that you can use for education credits is the total amount of
tuition and fees paid (box 2 on the 1098) minus the amount of grants or
scholarships (box 5 on the 1098) minus any amounts directly paid for by
the employer, or reimbursed by the employer.
See IRS Topic 513 - Educational Expenses for further discussion: http://www.irs.gov/taxtopics/tc513.html