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 $14.63   10.381%   $16.1487   $16.15   $16.15   $16.10  
  Purchase #2 $185.80   4.217%   $193.6352   $193.64   $193.65   $193.60  
  Purchase #3 $76.45   11.483%   $85.2288   $85.23   $85.25   $85.20  
  Purchase #4 $232.64   11.843%   $260.1916   $260.19   $260.20   $260.20  
  Purchase #5 $208.90   3.827%   $216.8946   $216.89   $216.90   $216.90  
  Purchase #6 $15.78   4.386%   $16.4721   $16.47   $16.45   $16.50  
  Purchase #7 $242.34   7.795%   $261.2304   $261.23   $261.25   $261.20  
  7 purchase totals = $976.54       $1,049.8014   $1,049.80   $1,049.85   $1,049.70