There's a reason for the "metric" measurement of displacement to almost always be "close", and the "American" measurement to be spot on.
Euroland, Asia and just about everywhere in between, where they use the metric system long before the US would even recognize it, started taxing vehicles by displacement about the time the 2nd one came off the assembly line, building for the tax break line and shaving a piston or thickening a gasket to just squeak below the next tax bracket. The norm of rounding to the nearest liter can also be attributed to the relatively small unit a cc is, it's 1000th of a liter, so a couple cc's here and there don't represent much, even less in the early days of less than efficient engine designs.
The US has never taxed displacement, and up until the last 25 years or so, always used Cubic Inches to measure displacement. There was no rounding up or down, as can be witnessed by the many engines referred to by their displacement, the 327, 318, 351 etc.
1 cubic inch = 16.387 cubic centimeters.
While not taxed, horsepower was a major factor in insurance rates for vehicles in the US, manufacturers have fudged official HP figures downward to assist in sales. Ford did this famously on the S Cobra Jet engines, officially rated at around 375HP for insurance purposes, they were actually delivered with around 450HP.