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 $56.95   8.597%   $61.846   $61.85   $61.85   $61.80  
  Purchase #2 $26.49   3.403%   $27.3915   $27.39   $27.40   $27.40  
  Purchase #3 $15.86   3.808%   $16.4639   $16.46   $16.45   $16.50  
  Purchase #4 $201.57   11.441%   $224.6316   $224.63   $224.65   $224.60  
  Purchase #5 $111.81   7.559%   $120.2617   $120.26   $120.25   $120.30  
  Purchase #6 $17.99   10.517%   $19.882   $19.88   $19.90   $19.90  
  Purchase #7 $220.91   5.771%   $233.6587   $233.66   $233.65   $233.70  
  7 purchase totals = $651.58       $704.1354   $704.13   $704.15   $704.20