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 $127.27   10.607%   $140.7695   $140.77   $140.75   $140.80  
  Purchase #2 $195.47   5.226%   $205.6853   $205.69   $205.70   $205.70  
  Purchase #3 $198.84   12.504%   $223.703   $223.70   $223.70   $223.70  
  Purchase #4 $232.91   12.477%   $261.9702   $261.97   $261.95   $262.00  
  Purchase #5 $175.78   7.660%   $189.2447   $189.24   $189.25   $189.20  
  Purchase #6 $125.55   5.651%   $132.6448   $132.64   $132.65   $132.60  
  Purchase #7 $214.88   10.477%   $237.393   $237.39   $237.40   $237.40  
  7 purchase totals = $1,270.70       $1,391.4105   $1,391.40   $1,391.40   $1,391.40