I too would like to see Moodle introduce functionality to easily round up fractional percentages in the grading scale since that is my policy for the CIS courses I teach at Northern Michigan University. In the interim, I accomplish this by using a level of indirection that actually stores the rounded values, as follows:
(1) Using Simple or Full view within Grade Administration, create a new category, giving it a Category Total Name of "Course Average," for example, and an ID Number, such as “couravg." Use the Move "action" to nest within this category all other categories and grade items. (2) Edit the main category for the entire course, setting the Category Total Name to "Course Letter Grade" and its Grade Display Type to "Letter(real)," initially, to test whether actual rounding occurs. Edit Calculation for Course Letter Grade, inserting formula =round(couravg, 0). After verifying rounding really worked, reset Grade Display Type to "Letter" to simlify the display in User Report.
Here is an example of what the student sees, correctly rounded: on the next-to-last line "Course Average 79.50" and on the last line "Course Letter Grade B-"