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 $58.62   9.341%   $64.0957   $64.10   $64.10   $64.10  
  Purchase #2 $205.73   13.591%   $233.6908   $233.69   $233.70   $233.70  
  Purchase #3 $239.31   9.174%   $261.2643   $261.26   $261.25   $261.30  
  Purchase #4 $40.92   12.758%   $46.1406   $46.14   $46.15   $46.10  
  Purchase #5 $169.71   3.844%   $176.2337   $176.23   $176.25   $176.20  
  Purchase #6 $140.80   12.358%   $158.2001   $158.20   $158.20   $158.20  
  Purchase #7 $78.50   6.543%   $83.6363   $83.64   $83.65   $83.60  
  7 purchase totals = $933.59       $1,023.2615   $1,023.26   $1,023.30   $1,023.20