Physics: Where did the energy go

A lab experiment for the conservation of energy theory resulted in E-initial being 0.625 and E-final being 0.610, therefore a 2.4% energy loss results. If the theory is that energy is neither created nor destroyed, where did this energy go? How do I explain it? is it a measuring mistake by one of the devices, or does friction/air resistance "eat" some of it up?

Lab set up

incline ramp, push cart up, motion sensor measures time and distance, computer records date, manipulate data to produce KE and PE, and KE and PE to get total E.

losses usually go into heat. The energy is not destroyed, it is converted to heat.

In this case it is friction of the wheels, the axles, and air resistance.

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A cart??? Are the wheels rotating? Are there wheels or is it on an air track? If it has wheels then you are losing some of it to the wheels rotating. In order to include that, you have to know something about moment of inertia. There is some friction, but I wouldn't say it's much and air resistance over such a small distance is inconsequential.

As an aside a 2.5% error in physics is absolutely fantastic. I used to tell my students that if it stinks it's chemistry and if it crawls it's Zoology and if nothing ever works out right, it's physics. I never saw results this good until our school sprang for an air track.

Edit
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I read some of the other answers and if your cart has ball bearings, and they are oiled, not much is going to go into heat over a short distance, but it is possible. I'll stick with 2.4 % being pretty good.

Energy conservation is always obeyed. In an experiment, you always (almost always) loose energy in friction, sound, heat etc.