DIY rounding function gives weird values [duplicate] - flutter

Question

This question already has answers here:
How do you round a double in Dart to a given degree of precision AFTER the decimal point?
(28 answers)
Closed 10 months ago.
I've coded this simple function to round doubles to a custom step size.
The normal .round() function retuns an int and can only rounds to the nearest 1.
My function returns a double and can round to the nearest 100.0, 5.0, 1.0, 0.1 or 0.23, you get it.
But when I put in certain doubles the result doesn't really work out and is a very tiny fraction off.
I think this has something to do with how computers do floating comma calcualations, but I need an efficient way to get around it.
Run on DartPad
void main() {
stepround(61.337551616741315, 0.1); // this should be 61.3 but is 61.300000000000004
}
/// rounds a double with given steps/precision
double stepround(double value, double steps) {
double rounded = (value / steps).round() * steps;
print(value.toString() + " rounded to the nearest " + steps.toString() + " is " + rounded.toString());
return rounded;
}

Answer 1

As mentioned in the comments, the cause of this issue the way that computers deal with floating numbers. Please refer to the links in the comments for further explanation.
However in a nutshell the problem is mostly caused when dividing or multiplying decimals with decimals. Therefore we can create a similar method to the one you created but with a different approach. We we will take the precision to be as an int.
I.e: 0.1 => 10; 0.001 => 1000
double stepround(double value, int place){
return (value * place).round() / place;
}
Example
// This will return 61.3
stepround(61.337551616741315, 10);
// This will return 61.34
stepround(61.337551616741315, 100);
// This will return 61.338
stepround(61.337551616741315, 1000);
This method works since the small fraction that is caused by the multiplication is removed by round(). And after that we are doing a division by an integer which doesn't create such a problem.