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 $61.85   9.229%   $67.5581   $67.56   $67.55   $67.60  
  Purchase #2 $176.46   5.194%   $185.6253   $185.63   $185.65   $185.60  
  Purchase #3 $120.81   12.108%   $135.4377   $135.44   $135.45   $135.40  
  Purchase #4 $105.95   4.661%   $110.8883   $110.89   $110.90   $110.90  
  Purchase #5 $241.51   10.447%   $266.7405   $266.74   $266.75   $266.70  
  Purchase #6 $131.87   4.318%   $137.5641   $137.56   $137.55   $137.60  
  Purchase #7 $42.88   4.266%   $44.7093   $44.71   $44.70   $44.70  
  7 purchase totals = $881.33       $948.5233   $948.53   $948.55   $948.50