diff --git a/stoptime.rb b/stoptime.rb
index f8b1c79..7221dd7 100644
--- a/stoptime.rb
+++ b/stoptime.rb
@@ -349,12 +349,22 @@ module StopTime::Models
     belongs_to :task
     has_one :customer, :through => :task
 
+    before_validation :round_start_end
+
     # Returns the total amount of time, the duration, in hours (up to
     # 2 decimals only!).
     def hours_total
       ((self.end - self.start) / 1.hour).round(2)
     end
 
+    #########
+    protected
+
+    def round_start_end
+      self.start = round_time(self.start)
+      self.end = round_time(self.end)
+    end
+
     #######
     private