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 $232.72   11.711%   $259.9738   $259.97   $259.95   $260.00  
  Purchase #2 $169.51   13.396%   $192.2176   $192.22   $192.20   $192.20  
  Purchase #3 $179.85   8.627%   $195.3657   $195.37   $195.35   $195.40  
  Purchase #4 $164.62   5.345%   $173.4189   $173.42   $173.40   $173.40  
  Purchase #5 $42.33   11.443%   $47.1738   $47.17   $47.15   $47.20  
  Purchase #6 $92.86   7.290%   $99.6295   $99.63   $99.65   $99.60  
  Purchase #7 $71.46   4.193%   $74.4563   $74.46   $74.45   $74.50  
  7 purchase totals = $953.35       $1,042.2356   $1,042.24   $1,042.15   $1,042.30