iOS - close keyboard when button is pressed

I currently have a textfield, a picker, a button, and several textviews/labels.

The textfield prompts a number only keyboard, I want the keyboard to dismiss when the one button is pressed.

Here is a snippet of some of the code:

class ViewController: UIViewController, UITextFieldDelegate, UIPickerViewDataSource, UIPickerViewDelegate  {

    @IBOutlet weak var provincePicker: UIPickerView!

    @IBOutlet weak var calcButton: UIButton!

    @IBOutlet weak var incomeLabel: UITextView!

    @IBOutlet weak var salaryTextField: UITextField!
    @IBOutlet weak var beforeTax: UITextView!
    @IBOutlet weak var provincialTax: UITextView!
    @IBOutlet weak var federalTax: UITextView!
    @IBOutlet weak var afterTax: UITextView!

...

    override func viewDidLoad() {
  //  numberOnly()
         borders()
         super.viewDidLoad()
         provincePicker.dataSource = self
         provincePicker.delegate = self
    }

...

     @IBAction func calculateButton(sender: UIButton) {
         let formatter           = NSNumberFormatter()
         formatter.numberStyle   = NSNumberFormatterStyle.CurrencyStyle
         formatter.locale        = NSLocale(localeIdentifier: "en_CA")

         let index = provincePicker.selectedRowInComponent(0)

         switch(index) {
         case 0:
            calculate(abBrackets, rates: abRates)   //AB
         //cutting out code here
         dismissKeyboard()
      }

      func dismissKeyboard() {
         self.view.endEditing(true)
      }