You need to use Action.SendKeys command and pass a key code from here: https://github.com/SeleniumHQ/selenium/blob/master/dotnet/src/webdriver/Keys.c

// Send 'Tab' keystroke
var actions = WebDriver.Actions();
actions.SendKeys(String.fromCharCode(0xE004)).Perform();

If you need to send same keystroke several times you may do it as follows:

// Send 'Backspace' 5 times
var actions = WebDriver.Actions();
var key = String.fromCharCode(0xE003)
actions.SendKeys(key+key+key+key+key).Perform();

Rapise 8.0+

In Rapise 8.0 we've added Navigator.DoSendKeys that supports patterns of Global.DoSendKeys.

Navigator.DoSendKeys("{TAB}");
Navigator.DoSendKeys("{BACKSPACE}");
Navigator.DoSendKeys("{ENTER}");