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 $86.36   13.103%   $97.6758   $97.68   $97.70   $97.70  
  Purchase #2 $58.69   10.572%   $64.8947   $64.89   $64.90   $64.90  
  Purchase #3 $126.87   7.677%   $136.6098   $136.61   $136.60   $136.60  
  Purchase #4 $66.65   7.859%   $71.888   $71.89   $71.90   $71.90  
  Purchase #5 $16.46   6.870%   $17.5908   $17.59   $17.60   $17.60  
  Purchase #6 $17.41   11.355%   $19.3869   $19.39   $19.40   $19.40  
  Purchase #7 $206.70   6.486%   $220.1066   $220.11   $220.10   $220.10  
  7 purchase totals = $579.14       $628.1526   $628.16   $628.20   $628.20