Rounding to nickel formula...

Question

Hi,
I have a formula for rounding a value to the nearest nickel. It seem that it does'nt work propably. The value of tempCalc after calculation is 3245.421123 and the result should be 3245.40 but I receive 3245.45 instead.
// round to the closest nickel (0.12 ==> 0.10 and 0.13 ==> 0.15)
private double RoundToNickel(double amontValue)
double tempCalc;
int modCalc;
tempCalc = ((double)(Math.round(amontValue*100)));
modCalc = (int) tempCalc % 5;
switch (modCalc)
case 1:
tempCalc = (tempCalc / 100) - .01 ;
break;
case 2:
tempCalc = (tempCalc / 100) - .02;
break;
case 3:
tempCalc = (tempCalc / 100) + .02;
break;
case 4:
tempCalc = (tempCalc / 100) + .01;
break;
default:
tempCalc = tempCalc / 100;
break;
tempCalc = ((double)(Math.round(tempCalc*100)))/100;
return tempCalc;
So I try the next one and the problem is that I receive 3245.40 but if I try with an other value I receive 3245.425 for example.
private double RoundToNickel(double amontValue)
double tempCalc;
// Test for rounding issues
double tempdouble;
// Determine the single cents
tempdouble = (amontValue * 10) % 1;
tempdouble = ((double)(Math.round(tempdouble * 1000)))/1000;
if (tempdouble > .5) {
tempCalc = amontValue + (((.5-tempdouble)* -1)/10);
} else {
tempCalc = amontValue - (tempdouble / 10) ;
return tempCalc;
Is there someone who can help me with this.

Answer 1

This should be what you want. Note that I coded it using binary floating point throughout, which is the cause of the "unusual" format of the results. This can be cured by formatting the results with DecimalFormat class.
There is a very small (by finite) possibility that an input will disrupt the code, again due to the imprecision of binary floating point numbers in representing decimal numbers. This probablilty can probably be ignored for practical purposes.
for(x = 0; x < 21; x++)
//-------Code starts here. Provide a value for inout.
double input = .01*x;
double nickels = input * 20;
double roundedNickels = (nickels - (int)nickels < .5) ? Math.floor(nickels) : Math.ceil(nickels);
double roundedOutput = roundedNickels * .05;
//-------roundedOutput contains the rounding of the input to the nearest .05
System.out.println("Input = " + input + "  Result = " + roundedOutput);
}For illustration purposes I placed the code in a loop and printed the following results:
Input = 0.0 Result = 0.0
Input = 0.01 Result = 0.0
Input = 0.02 Result = 0.0
Input = 0.03 Result = 0.05
Input = 0.04 Result = 0.05
Input = 0.05 Result = 0.05
Input = 0.06 Result = 0.05
Input = 0.07 Result = 0.05
Input = 0.08 Result = 0.1
Input = 0.09 Result = 0.1
Input = 0.1 Result = 0.1
Input = 0.11 Result = 0.1
Input = 0.12 Result = 0.1
Input = 0.13 Result = 0.15000000000000002
Input = 0.14 Result = 0.15000000000000002
Input = 0.15 Result = 0.15000000000000002
Input = 0.16 Result = 0.15000000000000002
Input = 0.17 Result = 0.15000000000000002
Input = 0.18 Result = 0.2
Input = 0.19 Result = 0.2
Input = 0.2 Result = 0.2