With the release of Unreal Engine version 4.1, we've updated the EULA to accommodate this low-revenue situation:

Now, the first $3000 of gross revenue per product per quarter is exempt from royalties. And, if gross revenue is less than $3000 in a given quarter, then you don't need to file a royalty report.

So, for example, if your game makes $2500 in a quarter, then you don't have to pay anything or file a report. If your game makes $4000, then the royalty due is $50, which is 5% of ($4000 minus $3000).