Project actual cost for hourly resources working OT

For those that bill the hours entered on a project, how do you handle when a resource works overtime on the project to get the actual cost of those hours on the project? 

For example - if an hourly resource with a cost of $20.00 / Hour works 10 hours on a project, with 2 of those hours being overtime, how do you get the actual cost to be $220, rather than $200.

I'm hoping someone has a "solution" for this that they have been using and will share. 

Thanks, 

Alex