I really love the question.
Think of it like like Bitcoin and Satoshi. You can own 0.00001 Bitcoin because Bitcoin relative to cash is nearly 100k and the existence of decimalization allows someone to pay below $1 for anything. This was the genius of 0. There is a whole history on zero’s introduction to European commerce.
Your bank however is unwilling to allow you to fractionalize your Dollar amounts below 1.00 (2 decimal places). In the currency exchange world where a one lot trade is equivalent to $100k then a small change in the value of one currency to the next can carry significant value. So it became essential to add 2 to 3 more decimal places to capture this value change.
That’s all it is. In FX of course the minimum change that overcomes spread cost is to the 4th decimal place (a pip) or to the 5th decimal place (pipette) in a zero spread environment. Hope this added clarity.
PS: If one day we can pay 0.001c for an item then I will assume central banking ended and interest on all money was abolished. (This is what Bitcoin thought it was about till JP Morgan sneezed Lol!)