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 $123.60   7.397%   $132.7427   $132.74   $132.75   $132.70  
  Purchase #2 $72.93   5.233%   $76.7464   $76.75   $76.75   $76.70  
  Purchase #3 $215.69   11.561%   $240.6259   $240.63   $240.65   $240.60  
  Purchase #4 $103.38   10.481%   $114.2153   $114.22   $114.20   $114.20  
  Purchase #5 $199.66   7.635%   $214.904   $214.90   $214.90   $214.90  
  Purchase #6 $142.86   3.410%   $147.7315   $147.73   $147.75   $147.70  
  Purchase #7 $41.65   11.616%   $46.4881   $46.49   $46.50   $46.50  
  7 purchase totals = $899.77       $973.4539   $973.46   $973.50   $973.30