Formatting Variable into Currency Format INSIDE script

Question

Hello, 
I was wondering if someone could give me insight on why I'm running into some problems.
So, in my script, I'm trying to display my [decimal]$Variable into currency format ( $x.xx ) 
By looking around online, I found two different ways;
"{0:C2}" -f $Variable will create the appropriate output in my open shell
$Variable.ToString("c") will also work in my shell. 
Now my only problem is that despite numerous attempts and quadrouple checking that I typed it into the ISE properly, I can't for the life of me get it to display properly in my script. 
I even just tried saving the output into a variable before I put it into my write-host line.
Does anyone know what the problem is? 
Thanks, Phil

Answer 1

$TaxPayable.ToString("c") | Set-Variable -Name $TaxInCurrency 
$TotalCost.ToString("c") | Set-Variable -Name $TotalCostInCurrency
##########################Display the $TaxPayable and $TotalCost to the user###################################
  Write-Host "The Tax for the Book is $TaxInCurrency, making the total cost $TotalCostInCurrency"
This is my latest attempt to make it work. Sorry about the initial lack of information