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 $230.95   13.265%   $261.5855   $261.59   $261.60   $261.60  
  Purchase #2 $205.83   4.523%   $215.1397   $215.14   $215.15   $215.10  
  Purchase #3 $117.95   11.390%   $131.3845   $131.38   $131.40   $131.40  
  Purchase #4 $140.37   11.130%   $155.9932   $155.99   $156.00   $156.00  
  Purchase #5 $246.27   6.169%   $261.4624   $261.46   $261.45   $261.50  
  Purchase #6 $199.99   7.416%   $214.8213   $214.82   $214.80   $214.80  
  Purchase #7 $114.37   9.837%   $125.6206   $125.62   $125.60   $125.60  
  7 purchase totals = $1,255.73       $1,366.0072   $1,366.00   $1,366.00   $1,366.00