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 $66.31   10.663%   $73.3806   $73.38   $73.40   $73.40  
  Purchase #2 $153.68   5.246%   $161.7421   $161.74   $161.75   $161.70  
  Purchase #3 $114.59   5.138%   $120.4776   $120.48   $120.50   $120.50  
  Purchase #4 $230.40   13.538%   $261.5916   $261.59   $261.60   $261.60  
  Purchase #5 $240.91   11.418%   $268.4171   $268.42   $268.40   $268.40  
  Purchase #6 $135.87   7.662%   $146.2804   $146.28   $146.30   $146.30  
  Purchase #7 $216.67   4.549%   $226.5263   $226.53   $226.55   $226.50  
  7 purchase totals = $1,158.43       $1,258.4157   $1,258.42   $1,258.50   $1,258.40