We’d need the code for ShushAppHelper::displayCurrency to help you.
But in your example that works to give you $10.00 the price is the first argument, and -3 the second argument.
In your next two attempts you made price the second argument.
The third one is wrong, because you have -2 inside the function call to [fphp]floor[/fphp]
Should ShushAppHelper::displayCurrency() ALWAYS round up to the nearest dollar when the cents are 00?
If so then, show us what that method does.
If the answer is possibly in this case only ShushAppHelper::displayCurrency() should round up, or ShushAppHelper is from a 3rd party codebase, then you should tackle this job as close to the output as possible and leave well enough alone.