Now, it's been a very long time since I see a mention of "Internet Explore 5". Kudos for highlighting the support for it but does it matter, who in the world are still using Internet Explorer 5?
IE5 was never a relevant contemporary of npm. The one that cast a long shadow on the web was IE6, pretty much exclusively, due to the unusual circumstances around antitrust intervention in the US and Europe putting MS off of really pushing their browser for nearly a decade (IE7 was pretty much DOA). IE5 was quickly replaced by IE6; nobody cared about it much even in 2005, let alone 2015. That was already an age of Chrome-first dev, complaining about Apple's lagging support for web ""standards"", and Firefox I guess more relevant than today but already increasingly an afterthought. The IE you'd be targeting, if any, was probably 8, unless you knew you wanted the userbase that was stuck with IE6.
A decade ago (2014) IE5 was completely dead. Some people were still force to care about IE6 but it was marginal. The default browser from that period was IE9 !