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 $250.68   7.154%   $268.6136   $268.61   $268.60   $268.60  
  Purchase #2 $13.32   3.836%   $13.831   $13.83   $13.85   $13.80  
  Purchase #3 $242.73   7.844%   $261.7697   $261.77   $261.75   $261.80  
  Purchase #4 $120.36   4.651%   $125.9579   $125.96   $125.95   $126.00  
  Purchase #5 $95.46   11.285%   $106.2327   $106.23   $106.25   $106.20  
  Purchase #6 $25.99   9.690%   $28.5084   $28.51   $28.50   $28.50  
  Purchase #7 $56.85   10.477%   $62.8062   $62.81   $62.80   $62.80  
  7 purchase totals = $805.39       $867.7195   $867.72   $867.70   $867.70