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 $66.96   13.432%   $75.9541   $75.95   $75.95   $76.00  
  Purchase #2 $227.72   13.133%   $257.6265   $257.63   $257.65   $257.60  
  Purchase #3 $109.37   6.559%   $116.5436   $116.54   $116.55   $116.50  
  Purchase #4 $77.75   8.535%   $84.386   $84.39   $84.40   $84.40  
  Purchase #5 $135.83   3.514%   $140.6031   $140.60   $140.60   $140.60  
  Purchase #6 $132.48   12.124%   $148.5419   $148.54   $148.55   $148.50  
  Purchase #7 $112.80   8.865%   $122.7997   $122.80   $122.80   $122.80  
  7 purchase totals = $862.91       $946.4549   $946.45   $946.50   $946.40