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 $65.84   3.803%   $68.3439   $68.34   $68.35   $68.30  
  Purchase #2 $199.69   5.862%   $211.3958   $211.40   $211.40   $211.40  
  Purchase #3 $85.73   9.803%   $94.1341   $94.13   $94.15   $94.10  
  Purchase #4 $59.91   10.621%   $66.273   $66.27   $66.25   $66.30  
  Purchase #5 $44.86   5.713%   $47.4229   $47.42   $47.40   $47.40  
  Purchase #6 $196.51   9.706%   $215.5833   $215.58   $215.60   $215.60  
  Purchase #7 $169.82   3.650%   $176.0184   $176.02   $176.00   $176.00  
  7 purchase totals = $822.36       $879.1714   $879.16   $879.15   $879.10