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 $241.76   10.253%   $266.5477   $266.55   $266.55   $266.50  
  Purchase #2 $115.48   7.773%   $124.4563   $124.46   $124.45   $124.50  
  Purchase #3 $82.48   3.395%   $85.2802   $85.28   $85.30   $85.30  
  Purchase #4 $151.93   11.682%   $169.6785   $169.68   $169.70   $169.70  
  Purchase #5 $249.84   4.769%   $261.7549   $261.75   $261.75   $261.80  
  Purchase #6 $147.61   11.857%   $165.1121   $165.11   $165.10   $165.10  
  Purchase #7 $233.34   6.210%   $247.8304   $247.83   $247.85   $247.80  
  7 purchase totals = $1,222.44       $1,320.6601   $1,320.66   $1,320.70   $1,320.70