If an employer matches 5% of your contribution, you can still, only meet the maximum. If Employer contributions exceed the max contribution allowed each individual, the money goes back to the employer.
An example of that is me; I contributed the maximum allowed of $22,000 off the top of my gross and the 5% Employer match had to be sent back to the employer in full. In fact, such programs reduce your 401K advantage because you cannot take as much off the gross income, which may put you into a higher bracket. The 5% employer contribution is added into the total each year, so you lose part of the advantage of a 401K.