4 Answers

The earth is not really round. Technically it IS a circle but it's not a perfect circle or using your wording, it is not perfectly round. It's a circle that's pushed out of shape because of it's fast rotation.  The earth is actually sphere shaped or to be more precise it's an oblate spheroid with a bulge at the equator. 

Gravitational pull……...

Without looking "it" up, my initial thought is the shape is convenient.  The earth spins on its axis and rotates in a circular motion around the sun, in its orbit.  

An earth shaped in any other form would have "issues" with this setup.  

b/c it spins more efficiently on it's axis when it's round. Like you can spin a basket ball on the end of your fingertip better than you can spin a box.