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 $24.44   6.544%   $26.0394   $26.04   $26.05   $26.00  
  Purchase #2 $115.82   11.545%   $129.1914   $129.19   $129.20   $129.20  
  Purchase #3 $103.51   12.702%   $116.6578   $116.66   $116.65   $116.70  
  Purchase #4 $226.81   7.672%   $244.2109   $244.21   $244.20   $244.20  
  Purchase #5 $167.99   10.702%   $185.9683   $185.97   $185.95   $186.00  
  Purchase #6 $109.76   4.301%   $114.4808   $114.48   $114.50   $114.50  
  Purchase #7 $248.71   9.697%   $272.8274   $272.83   $272.85   $272.80  
  7 purchase totals = $997.04       $1,089.3760   $1,089.38   $1,089.40   $1,089.40