The BRM guideline is more often stated as 20 buyins rather than 5%. There's a difference. If you're using 20 buyins, you must have at least $100 to sit at nl5. But if you shade this so it's 5%, you can sit with $4.75.
This isn't a large difference, but it's the first step down a slippery slope. For instance, what if your roll has dropped to $75? Is it okay to sit at nl5 by buying in for $3.75? And how far can you take this? $50 and $250? $25 and $1.25?
Fwiw, I usually suggest 30 buyins to move up, so $150 for nl5. And drop to a lower stake if you fall below 20 buyins, even a cent below. After all, if you had $150 and now have $99.99, you're not exactly crushing it. So better to go back to nl2 and rebuild to $150 (or more since 30x is a minimum, not a requirement to move up) so you're rolled to try again.