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 $135.71   10.296%   $149.6827   $149.68   $149.70   $149.70  
  Purchase #2 $197.68   4.792%   $207.1528   $207.15   $207.15   $207.20  
  Purchase #3 $226.49   12.798%   $255.4762   $255.48   $255.50   $255.50  
  Purchase #4 $40.77   9.571%   $44.6721   $44.67   $44.65   $44.70  
  Purchase #5 $51.35   10.260%   $56.6185   $56.62   $56.60   $56.60  
  Purchase #6 $203.99   13.292%   $231.1044   $231.10   $231.10   $231.10  
  Purchase #7 $44.63   12.543%   $50.2279   $50.23   $50.25   $50.20  
  7 purchase totals = $900.62       $994.9346   $994.93   $994.95   $995.00