Use a format string to round up to two decimal places and convert the double to a String:

let currentRatio = Double (rxCurrentTextField.text!)! / Double (txCurrentTextField.text!)!
railRatioLabelField.text! = String(format: "%.2f", currentRatio)

Example:

let myDouble = 3.141
let doubleStr = String(format: "%.2f", myDouble) // "3.14"

If you want to round up your last decimal place, you could do something like this (thanks Phoen1xUK):

let myDouble = 3.141
let doubleStr = String(format: "%.2f", ceil(myDouble*100)/100) // "3.15"

Convert it into a string with 2 digits after the decimal:

let yourShareString = String(format: "%.2f", yourShare)

//find the distance between two points
let coordinateSource = CLLocation(latitude: 30.7717625, longitude:76.5741449 )
let coordinateDestination = CLLocation(latitude: 29.9810859, longitude: 76.5663599)
let distanceInMeters = coordinateSource.distance(from: coordinateDestination)
let valueInKms = distanceInMeters/1000
let preciseValueUptoThreeDigit = Double(round(1000*valueInKms)/1000)
self.lblTotalDistance.text = "Distance is : \(preciseValueUptoThreeDigit) kms"

Use a format string to round up to two decimal places and convert the double to a String:

let currentRatio = Double (rxCurrentTextField.text!)! / Double (txCurrentTextField.text!)!
railRatioLabelField.text! = String(format: "%.2f", currentRatio)

Example:

let myDouble = 3.141
let doubleStr = String(format: "%.2f", myDouble) // "3.14"

If you want to round up your last decimal place, you could do something like this (thanks Phoen1xUK):

let myDouble = 3.141
let doubleStr = String(format: "%.2f", ceil(myDouble*100)/100) // "3.15"

As in most languages the format is

%.2f

you can see more examples here

Edit: I also got this if your concerned about the display of the point in cases of 25.00

{
    NSNumberFormatter *fmt = [[NSNumberFormatter alloc] init];
    [fmt setPositiveFormat:@"0.##"];
    NSLog(@"%@", [fmt stringFromNumber:[NSNumber numberWithFloat:25.342]]);
    NSLog(@"%@", [fmt stringFromNumber:[NSNumber numberWithFloat:25.3]]);
    NSLog(@"%@", [fmt stringFromNumber:[NSNumber numberWithFloat:25.0]]);
}

2010-08-22 15:04:10.614 a.out[6954:903] 25.34
2010-08-22 15:04:10.616 a.out[6954:903] 25.3
2010-08-22 15:04:10.617 a.out[6954:903] 25

If you want to really round the number, and not just format it as rounded for display purposes, then I prefer something a little more general-purpose:

extension Double {
    func rounded(digits: Int) -> Double {
        let multiplier = pow(10.0, Double(digits))
        return (self * multiplier).rounded() / multiplier
    }
}

So you can then do something like:

let foo = 3.14159.rounded(digits: 3) // 3.142

You can simply do this:

let pi = 3.14159

let text = String(format: "%.2f", arguments: [pi])

print(text) // output = 3.14

Double indeed has no method roundTo(places:). That‘s a method you would first have to implement yourself. To do that, see this answer, for example.

Or, if you don’t want to create a separate method, you could directly do this (inspired by the aforementioned answer):

let cost = (poundMonth * 100).rounded() / 100

BUT: If you don‘t need the rounded value for any further calculations, but want to display it to the user, NumberFormatter is the way to go. For example, it also offers localization. See this answer.