Best way to strip dollar amounts of unwanted characters

Hi,
I have a simple form with one field... 'discount'
My users may type all kinds of crazy variations unfortunately. I'm hoping to get a dependable way of stripping it to the actual amount they mean.

Possible input:
$12,932.99
or
12,999
or
12999
etc.

I need to round up to the closet dollar
Remove zeros after decimal (including the decimal)
Get rid of any dollar signs etc. that aren't numbers

I've tried a few variations with rtrim, regex, num_format etc. but can't pull it all together.
Hoping someone can assist.
Below is just one attempt :)

$discount = rtrim($request->input('discount'), "0");
$discount = preg_replace('/[^\d]+/', '', $discount);

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