Rounding up is common and considered good marketing. Governments may base vehicle taxes, by whatever name, on round numbered values, 100cc steps, 850cc and below, 3.0 liters and above, etc. Should you race your vehicle, racing classes are almost always set by round number displacements.
But this is the best answer, because pi's irrationality (it goes as many digits as you care to enumerate) and non-roundness make a 3.000 litre or 1.600 or any other round displacement difficult to hit within .5 CC of a target value. (0.5 / 1500 = 1/3000 = 0.000333...) Round number displacements mean making piston bores, piston diameters and/or crankshaft strokes with 5 digit precision, non-round, values. If you're making zillions of something, any dimension is as good as any other, although that +/-0.0001 part tolerance is going to cost real money.
As the orders fall from millions to thousands, getting suppliers to make (3.14159 X 25.4)mm parts, +/-0.01% gets expensive too. Training people setting up the machines, ordering stock material, is easier, if you're making 76.2mm pistons, compared to 79.796mm. US built engines used to have 3.000 or 4.000 inch pistons, +/- more than 0.001". Far easier to make an 1149cc motor and sell it as a "1200". That's a 0.5% difference. No big thing. Unless you're trying to hit 1200 +/ 0.5, where you need 1/2400, 0.0417%.