Your questions illustrate well the difficulty of handling all the calculated question parameters.
The Correct answer is calculated from the formula i.e. 55*10 = 550 which is the true value after
conversion using the settings of significant figures.
As I can deduced 550 is 5.5*102
which has been rounded to 1 digit i.e. 6 *102
and expressed as the Correct answer 600 that will be shown to the student once he answered the question.
However all the calculations and grading will be done with the true value i.e 550 +- 0.01 relative i.e. +-5.5 so you should get Min 545.5 Max 555.5.
However when PHP (or C) handle real numbers, they do not handle them perfectly as with integer.
There is a precision limit and this precision limit has been added to the grading limit so that the student always receive the best grade.
Here the precision limits seems to be 1 *10-11
giving the Min 544.499999999 and 555.50000000001
So edit your question and change your settings for Correct answer so that a sufficient number of figures are displayed in relation to your Tolerance settings.
In 2.0 these settings for Tolerance and Correct answer will be available in the page (Edit the datasets) to help solve those problems.