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 $58.81   8.677%   $63.9129   $63.91   $63.90   $63.90  
  Purchase #2 $143.79   6.294%   $152.8401   $152.84   $152.85   $152.80  
  Purchase #3 $167.73   12.550%   $188.7801   $188.78   $188.80   $188.80  
  Purchase #4 $132.54   10.211%   $146.0737   $146.07   $146.05   $146.10  
  Purchase #5 $85.66   3.505%   $88.6624   $88.66   $88.65   $88.70  
  Purchase #6 $27.48   5.794%   $29.0722   $29.07   $29.05   $29.10  
  Purchase #7 $249.42   10.298%   $275.1053   $275.11   $275.10   $275.10  
  7 purchase totals = $865.43       $944.4467   $944.44   $944.40   $944.50