Re: Rounding error
Except that I doubt whether a 200 mg Ibuprofen tablet is actually within half a milligram of that dose. There wouldn't be any point given that adult human body masses vary by a factor of two or more (depending on your definition of normal adult human). 200mg +/- 10% would be just fine. (Manufacturing accuracy is probably better than that without adding any cost). Scientists quote the amount without gratuitous extra digits, and the error separately. 1 gram or 1000 mg +/- 0.03g or 30mg is fine. 1000.0 mg +/- 30mg would be silly. 1000mg equals one gram and shouldn't imply anything about the error when no error is quoted.
Drugs for which a 50% extra dose is dangerous are unusual, and require individual prescriptions based on a patient's body mass and/or metabolic variables, also careful ongoing monitoring for toxicity. An ideal drug hits its maximum therapeutic effect at one dose and doesn't become toxic until a much higher dose. Ibuprofen (which I know about) maxes out at around 2400mg per day (a doctor-prescribable dose) and doesn't usually have serious toxicity issues at considerably higher doses ... it's just useless to take more. A greater danger is the long-term effect on your body of the drug doing exactly what it is supposed to do (ie suppressing inflammation).
Incidentally with many drugs (including Ibuprofen) it's safe to take a doubled first dose for a more rapid effect. That first dose finds your body "empty". When it's time for the next, half the original dose is still not present. The third dose finds a quarter of the first and half of the second ... Don't try this trick ("front-loading") without asking a doctor, or at least carefully checking the literature. There are exceptions.