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 $68.67   11.351%   $76.4647   $76.46   $76.45   $76.50  
  Purchase #2 $135.49   3.777%   $140.6075   $140.61   $140.60   $140.60  
  Purchase #3 $68.32   6.473%   $72.7424   $72.74   $72.75   $72.70  
  Purchase #4 $228.63   12.335%   $256.8315   $256.83   $256.85   $256.80  
  Purchase #5 $152.61   3.265%   $157.5927   $157.59   $157.60   $157.60  
  Purchase #6 $59.61   4.122%   $62.0671   $62.07   $62.05   $62.10  
  Purchase #7 $189.43   6.673%   $202.0707   $202.07   $202.05   $202.10  
  7 purchase totals = $902.76       $968.3766   $968.37   $968.35   $968.40