Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $114.44   3.562%   $118.5164   $118.52   $118.50   $118.50  
  Purchase #2 $182.80   7.741%   $196.9505   $196.95   $196.95   $197.00  
  Purchase #3 $114.63   13.240%   $129.807   $129.81   $129.80   $129.80  
  Purchase #4 $121.41   7.299%   $130.2717   $130.27   $130.25   $130.30  
  Purchase #5 $46.75   8.245%   $50.6045   $50.60   $50.60   $50.60  
  Purchase #6 $104.48   13.775%   $118.8721   $118.87   $118.85   $118.90  
  Purchase #7 $57.57   3.112%   $59.3616   $59.36   $59.35   $59.40  
  7 purchase totals = $742.08       $804.3838   $804.38   $804.30   $804.50