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 $151.67   3.614%   $157.1514   $157.15   $157.15   $157.20  
  Purchase #2 $214.47   4.663%   $224.4707   $224.47   $224.45   $224.50  
  Purchase #3 $157.38   10.312%   $173.609   $173.61   $173.60   $173.60  
  Purchase #4 $218.32   12.495%   $245.5991   $245.60   $245.60   $245.60  
  Purchase #5 $35.45   4.824%   $37.1601   $37.16   $37.15   $37.20  
  Purchase #6 $233.39   11.816%   $260.9674   $260.97   $260.95   $261.00  
  Purchase #7 $205.46   10.604%   $227.247   $227.25   $227.25   $227.20  
  7 purchase totals = $1,216.14       $1,326.2047   $1,326.21   $1,326.15   $1,326.30