Is there a tool that will make a rounded cut in flat metal wire? Is there a tool that can cut flat 5mm-wide aluminum jewelry wire to leave a rounded end? (An as-yet nonexistent extremely heavy duty nail clipper  comes to mind).
In the image below, the wire on the left is an example of what we started with. We've used a grinder to round the end of the wire on the right. If we could just cut it in a round shape and then polish the end, it would save a lot of metal dust about a minute of grinding per end (and we may have hundreds to do).

An answer to this other question mentioned the use of a deburring tool, which may be useful after making a round cut.
This metal piece helps snug a medical mask to a person's nose. We wanted it to be rounded to prevent it from breaking through the material. My wife is making medical masks for friends that are health care providers who are worried about the current mask shortage. Hers is a five layered design that I'll encourage her to post soon. Without this metal piece, air leaks around the nose.
UPDATE: &quot;Normal&quot; toenail clippers actually worked well enough. I hadn't thought about actually trying them, but after the accepted answer below suggested something we thought flimsier than toenail clippers, we went ahead and gave toenail clippers a try.
As you're only working in thin aluminium, I suggest a gouge chisel.  It will need sharpening fairly often (a diamond file is probably easiest) to go through easily but should do a good job.  Use scrapwood clamped down securely as your anvil.  

I don't have a gouge, but I've tested a straight chisel successfully. My scrap aluminium is 3mm thick and a cut of about 8mm long took a couple of blows with a carpenter's mallet on the back of my roughest (not very sharp, as well as chipped) chisel.  This is bigger than your cut, so you should be able to do it in a single blow.  An offcut of oak worktop was a much better anvil than softwood: the cut was easier and the burr on the back much less. If doing a lot you may wish to make a jig, or at least attach a fence/length guide.  

The heavy-duty nail clippers you were thinking of do exist, but I suspect that they'd push the strip out when you squeeze them.

There are also curved tin snips, but ones as curved as this old pair are rare nowadays.