I had to sort out how to manage a multi currency salesforce and a mono currency Marketo. So I copy the answer I did on these discussions :
"As Marketo manages only one currency, you need to convert all amounts coming from salesforce before they arrive in Marketo.
For this you have to create a custom field in the opportunity object that will contain the converted value based on your organization currency.
Here is a link that can help you do this in salesforce because it involves advanced skills
Then you can log a case and ask the support to remap the link between the opportunity amount in Marketo with your new field (after having cleaned all smart lists using the amount field as the remapping needs that the fields involved are not used). I also recommend saving all values for amount on opportunities in salesforce as the remapping can erase the values. You may need to reload tham after the remapping (the support can explain this better than me).
So then all your reporting will be based on the same currency.
Of course, you will have to input in Marketo all costs in your org. currency.
Hope it helps !!