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 $64.61   9.202%   $70.5554   $70.56   $70.55   $70.60  
  Purchase #2 $206.44   8.341%   $223.6592   $223.66   $223.65   $223.70  
  Purchase #3 $97.82   8.134%   $105.7767   $105.78   $105.80   $105.80  
  Purchase #4 $146.50   7.673%   $157.7409   $157.74   $157.75   $157.70  
  Purchase #5 $180.73   5.247%   $190.2129   $190.21   $190.20   $190.20  
  Purchase #6 $224.71   9.650%   $246.3945   $246.39   $246.40   $246.40  
  Purchase #7 $240.42   11.479%   $268.0178   $268.02   $268.00   $268.00  
  7 purchase totals = $1,161.23       $1,262.3574   $1,262.36   $1,262.35   $1,262.40