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 $242.95   10.527%   $268.5253   $268.53   $268.55   $268.50  
  Purchase #2 $225.37   10.765%   $249.6311   $249.63   $249.65   $249.60  
  Purchase #3 $106.88   7.243%   $114.6213   $114.62   $114.60   $114.60  
  Purchase #4 $200.43   5.213%   $210.8784   $210.88   $210.90   $210.90  
  Purchase #5 $117.76   12.169%   $132.0902   $132.09   $132.10   $132.10  
  Purchase #6 $149.34   8.414%   $161.9055   $161.91   $161.90   $161.90  
  Purchase #7 $145.40   10.630%   $160.856   $160.86   $160.85   $160.90  
  7 purchase totals = $1,188.13       $1,298.5078   $1,298.52   $1,298.55   $1,298.50