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 $56.43   5.789%   $59.6967   $59.70   $59.70   $59.70  
  Purchase #2 $208.83   13.462%   $236.9427   $236.94   $236.95   $236.90  
  Purchase #3 $236.53   5.261%   $248.9738   $248.97   $248.95   $249.00  
  Purchase #4 $89.90   8.378%   $97.4318   $97.43   $97.45   $97.40  
  Purchase #5 $21.40   9.548%   $23.4433   $23.44   $23.45   $23.40  
  Purchase #6 $193.88   6.376%   $206.2418   $206.24   $206.25   $206.20  
  Purchase #7 $115.65   12.305%   $129.8807   $129.88   $129.90   $129.90  
  7 purchase totals = $922.62       $1,002.6108   $1,002.60   $1,002.65   $1,002.50