Similar to rounding to 10, I want to round to any number

Similar to rounding to 10, I want to round to any number

 

var c = 38;
var b = 20;
var a = c / b == 0 ? 1 : c / b;
a = Math.round(a);
c = a * b;
               
 c=40

var c = 28;
var b = 20;
var a = c / b == 0 ? 1 : c / b;
a = Math.round(a);
c = a * b;
               
 c=20