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 $249.63   4.538%   $260.9582   $260.96   $260.95   $261.00  
  Purchase #2 $177.42   5.299%   $186.8215   $186.82   $186.80   $186.80  
  Purchase #3 $91.56   11.771%   $102.3375   $102.34   $102.35   $102.30  
  Purchase #4 $97.60   7.269%   $104.6945   $104.69   $104.70   $104.70  
  Purchase #5 $241.33   3.679%   $250.2085   $250.21   $250.20   $250.20  
  Purchase #6 $222.65   8.592%   $241.7801   $241.78   $241.80   $241.80  
  Purchase #7 $170.66   10.575%   $188.7073   $188.71   $188.70   $188.70  
  7 purchase totals = $1,250.85       $1,335.5076   $1,335.51   $1,335.50   $1,335.50