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 $235.29   11.272%   $261.8119   $261.81   $261.80   $261.80  
  Purchase #2 $114.69   9.130%   $125.1612   $125.16   $125.15   $125.20  
  Purchase #3 $236.67   11.322%   $263.4658   $263.47   $263.45   $263.50  
  Purchase #4 $174.56   11.314%   $194.3097   $194.31   $194.30   $194.30  
  Purchase #5 $136.80   11.609%   $152.6811   $152.68   $152.70   $152.70  
  Purchase #6 $234.92   6.206%   $249.4991   $249.50   $249.50   $249.50  
  Purchase #7 $106.66   8.665%   $115.9021   $115.90   $115.90   $115.90  
  7 purchase totals = $1,239.59       $1,362.8309   $1,362.83   $1,362.80   $1,362.90