

Masters in classics here. They literally are, even the number 4. Look at a watch with Roman numerals and notice that the 4 is “IIII”.
I = 1 finger
…
V = open hand
…
X = two open hands next to each other
Edit to add:
Why do you get “L” for 50 and “C” for 100? The C “centum” was written with two reversed “L” shapes. Take away half of that, and you are left with L.
Why do you get “M” for 1,000 and “D” for 500? Same reason–doubled up reversed D shapes. Take away half and you’re left with a D.
The ones sold in supermarkets are not the same as what are distributed to restaurants. Plus, you don’t have the right equipment to make it the same way as the restaurant.