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 $229.53   13.512%   $260.5441   $260.54   $260.55   $260.50  
  Purchase #2 $96.34   8.107%   $104.1503   $104.15   $104.15   $104.20  
  Purchase #3 $151.39   4.315%   $157.9225   $157.92   $157.90   $157.90  
  Purchase #4 $92.93   5.389%   $97.938   $97.94   $97.95   $97.90  
  Purchase #5 $116.54   8.592%   $126.5531   $126.55   $126.55   $126.60  
  Purchase #6 $96.74   13.359%   $109.6635   $109.66   $109.65   $109.70  
  Purchase #7 $101.48   13.495%   $115.1747   $115.17   $115.15   $115.20  
  7 purchase totals = $884.95       $971.9462   $971.93   $971.90   $972.00