[rezonant]

This would be a good dbrand style marketing point; "Round down pricing: You're a rounding error, so why would we bother charging you!" :-)

[vidyesh]

Their end of the month email is

Good news from Fly.io! We don’t collect bills smaller than $5.00.

This month, your bill of $2.01 falls below that threshold, so we’re discounting it by 100%.