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 $236.52   7.324%   $253.8427   $253.84   $253.85   $253.80  
  Purchase #2 $52.54   6.252%   $55.8248   $55.82   $55.80   $55.80  
  Purchase #3 $104.45   8.786%   $113.627   $113.63   $113.65   $113.60  
  Purchase #4 $104.49   11.344%   $116.3433   $116.34   $116.35   $116.30  
  Purchase #5 $44.82   7.240%   $48.065   $48.07   $48.05   $48.10  
  Purchase #6 $196.50   12.725%   $221.5046   $221.50   $221.50   $221.50  
  Purchase #7 $38.67   10.311%   $42.6573   $42.66   $42.65   $42.70  
  7 purchase totals = $777.99       $851.8647   $851.86   $851.85   $851.80