fix: --fail-under=100 could report 100 is less than 100.

Use the same rounding rules for the fail-under message that are used for totals
everywhere else, so that it won't say:

    total of 100 is less than fail-under=100

1 files changed, 17 insertions, 7 deletions

diff --git a/coverage/results.py b/coverage/results.py
index c60ccac2..f7331b41 100644
--- a/coverage/results.py
+++ b/coverage/results.py
@@ -219,14 +219,24 @@ class Numbers(SimpleReprMixin):
         result in either "0" or "100".
 
         """
-        pc = self.pc_covered
-        if 0 < pc < self._near0:
-            pc = self._near0
-        elif self._near100 < pc < 100:
-            pc = self._near100
+        return self.display_covered(self.pc_covered)
+
+    @classmethod
+    def display_covered(cls, pc):
+        """Return a displayable total percentage, as a string.
+
+        Note that "0" is only returned when the value is truly zero, and "100"
+        is only returned when the value is truly 100.  Rounding can never
+        result in either "0" or "100".
+
+        """
+        if 0 < pc < cls._near0:
+            pc = cls._near0
+        elif cls._near100 < pc < 100:
+            pc = cls._near100
         else:
-            pc = round(pc, self._precision)
-        return "%.*f" % (self._precision, pc)
+            pc = round(pc, cls._precision)
+        return "%.*f" % (cls._precision, pc)
 
     @classmethod
     def pc_str_width(cls):