There is no indication that 5% of the population will die.
The Imperial College report finds that in a complete do-nothing scenario, 4 million Americans will die, which is only 1.2% of the population.
With some mitigation (isolation of the elderly, isolation of suspect cases and their families) that number is reduced to 2 million, only 0.6% of the total population. This is the approach we need to be pursuing, and it means reopening all schools and businesses right now, and directing and supporting the elderly to self-isolate. Massively ramping up our healthcare infrastructure and preparing for massive triage is also a good idea.
The alternative of complete suppression requires total shutdown for an estimated period of 18 months, until a vaccine is available. However, its worth nothing that vaccines for influenza (for reference) are only partially (50-70%) effective, and need to be renewed annually. So its likely that even in this total shutdown scenario, we are still looking at 1 million deaths - with immense and unprecedented economic and social impacts.
Keep in mind, that 2.8 million Americans die annually from all causes - 0.8%. Coronavirus might mean for example that a critically ill patient dies from cancer a week earlier than otherwise.