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 $73.66   3.403%   $76.1666   $76.17   $76.15   $76.20  
  Purchase #2 $208.37   10.644%   $230.5489   $230.55   $230.55   $230.50  
  Purchase #3 $66.39   13.486%   $75.3434   $75.34   $75.35   $75.30  
  Purchase #4 $56.30   8.814%   $61.2623   $61.26   $61.25   $61.30  
  Purchase #5 $190.56   6.383%   $202.7234   $202.72   $202.70   $202.70  
  Purchase #6 $247.57   8.131%   $267.6999   $267.70   $267.70   $267.70  
  Purchase #7 $113.30   8.137%   $122.5192   $122.52   $122.50   $122.50  
  7 purchase totals = $956.15       $1,036.2637   $1,036.26   $1,036.20   $1,036.20