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 $59.76   7.252%   $64.0938   $64.09   $64.10   $64.10  
  Purchase #2 $198.26   13.309%   $224.6464   $224.65   $224.65   $224.60  
  Purchase #3 $59.72   8.258%   $64.6517   $64.65   $64.65   $64.70  
  Purchase #4 $103.72   10.370%   $114.4758   $114.48   $114.50   $114.50  
  Purchase #5 $90.56   7.806%   $97.6291   $97.63   $97.65   $97.60  
  Purchase #6 $223.88   7.324%   $240.277   $240.28   $240.30   $240.30  
  Purchase #7 $70.79   3.739%   $73.4368   $73.44   $73.45   $73.40  
  7 purchase totals = $806.69       $879.2106   $879.22   $879.30   $879.20