New to oracle. I do not get the concept of round function. It seems to be silly.

select round(50.989, -2) from dual ;
gives the result as 100.

select round(50.989, -1) from dual;
gives the result as 50.

I think I didn't understand the definition properly.

When I give select round(12.989, -1) from dual;
gives 10.

could somone kindly explain this.

thank you