Determining Data Type Of Argument In Custom Function

In VBA, True takes the integer value of -1. However, in Excel, it is 1.

I am writing a custom function that does arithmetic on a value. However, due to above, if the value is True, my custom function produces a different result than if I wrote an Excel formula to do the same thing.

Is there some way to identify the data type of a value passed into a function? Currently my function looks like this:

' Return the valueToIncrement with its magnitude increased by PctToAdd
Public Function INCREMENTPCT(valueToIncrement As Variant, PctToAdd As Variant) As Variant

INCREMENTPCT = valueToIncrement * (1 + PctToAdd)

End Function

Ideally I would like to identify whether the type is Boolean and adjust the value so as to give the same result as an Excel formula would give.