lowering my power

Hi,

I want to buy circle lenses online the only availabe for my power is -5.50 they do not have -5.75 which is my a ctual power on both eye. i asked the website about this and they told me it wouldn't make a difference if i lowered my power since its not much of a difference they said no harm would be done.
my question is would it hurt my eyes if i lowerd my power? would i have any problems with it? is it really much of a difference?

please  get back to me as soon as possible.

thank you.