you don't have to add a SINGLE product with that price, but all the articles in the first post!!

Anyway you can replicate the issue with just one:

Add a product with base price 4.54545.
Add an order from the backend of 3 of the above items generates a row total of 16.49, while the raw math is:
4.54545 * 3 * 1.21 -> 16,4999835. The above value should be 16.50, then...

any update on this?

at least, how can we trigger VMInvoice calculations?

we fixed with the following options:

1. set all roundings to -1 in VM Config, except the last one
2. enable "Round only on display" in VM config (again in the Prices tab like above)
3. disable prices rounding in tax summary in VMInvoice (Invoice item options)