Nah, the roman system developed from even older systems.

They're tally marks, with a twist.

You take a stick and cut a notch, that's one. This works up to a point, and that point is 4 or 5, when it becomes unwieldy, and our brains have trouble using the groups of notches.

So you need a new mark to denote a grouping. The v notch is basically adding a / to the already present \ or | tally mark, denoting that the new symbol represents a group of the previous ones.

Different methods have 3 base marks, with the fourth being the new one, others do it at five.

Roman numerals stop at 3 individual marks, and there's no record of why. But avoiding 4 repeating symbols is consistent with the higher numerals as well.

Basically, once you hit |||, the next number with be the | subtracted from the next higher digit. It works with IX, as well as XL, XC, etc.

But, the idea you suggest is sometimes presented as a possible origin for the earlier systems. Thing is, other tally systems that originated separately follow the same basic concepts, without using the same V symbol, but using other cross marks. Not that it matters because nobody knows. Nobody back then passed the information along.

It does kinda make sense, but the idea that it's the simplest way to make marks on sticks and stones does too

I've never heard of crossing your fingers like that to indicate 10.

Many archaic cultures had words for 1, 2, 3, and "many". You can see this tendency reflected in the Roman system where I, II, and III are obvious symbols, but IV introduces two new concepts: V for five, and the system where putting a symbol to the left represents that much less than the next symbol.

Therefore I think 1, 2, and 3 are based on counting on fingers, but 4 is where their system deviates.