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 $92.44   5.399%   $97.4308   $97.43   $97.45   $97.40  
  Purchase #2 $236.77   8.522%   $256.9475   $256.95   $256.95   $256.90  
  Purchase #3 $151.52   12.546%   $170.5297   $170.53   $170.55   $170.50  
  Purchase #4 $158.54   6.578%   $168.9688   $168.97   $168.95   $169.00  
  Purchase #5 $94.97   3.454%   $98.2503   $98.25   $98.25   $98.30  
  Purchase #6 $22.61   3.861%   $23.483   $23.48   $23.50   $23.50  
  Purchase #7 $109.27   4.683%   $114.3871   $114.39   $114.40   $114.40  
  7 purchase totals = $866.12       $929.9972   $930.00   $930.05   $930.00