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 $62.63   12.324%   $70.3485   $70.35   $70.35   $70.30  
  Purchase #2 $146.81   4.854%   $153.9362   $153.94   $153.95   $153.90  
  Purchase #3 $10.61   6.517%   $11.3015   $11.30   $11.30   $11.30  
  Purchase #4 $117.87   12.396%   $132.4812   $132.48   $132.50   $132.50  
  Purchase #5 $77.67   5.194%   $81.7042   $81.70   $81.70   $81.70  
  Purchase #6 $163.43   5.158%   $171.8597   $171.86   $171.85   $171.90  
  Purchase #7 $177.32   13.298%   $200.9   $200.90   $200.90   $200.90  
  7 purchase totals = $756.34       $822.5313   $822.53   $822.55   $822.50