Javascript Maths

I am adding numbers from text boxes on a form using javascript. I was using parse int but this caused problems when adding decimals. I am know using parsefloat, this works but occasionally I will get a number that is more than 2 decimal places, is there anyway of showing the number as two decimal places.

var x,y,z,a;
x = 12.345;
y = 67.89;
z = x*y;
// adding 0.005 to simulate a round()
// parseInt just chops off everything following the .
a = parseInt(100*(z+0.005))/100;

this will show numbers with at most 2 decimals

when you want exactly 2 decimals, you should use strings
possible in combination with above solution
(convert to string, check length after dot, append 0,1,2 zero's)