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 $248.39   5.157%   $261.1995   $261.20   $261.20   $261.20  
  Purchase #2 $9.82   7.861%   $10.592   $10.59   $10.60   $10.60  
  Purchase #3 $117.29   13.589%   $133.2285   $133.23   $133.25   $133.20  
  Purchase #4 $198.28   11.151%   $220.3902   $220.39   $220.40   $220.40  
  Purchase #5 $160.64   3.121%   $165.6536   $165.65   $165.65   $165.70  
  Purchase #6 $19.37   7.439%   $20.8109   $20.81   $20.80   $20.80  
  Purchase #7 $176.77   4.636%   $184.9651   $184.97   $184.95   $185.00  
  7 purchase totals = $930.56       $996.8398   $996.84   $996.85   $996.90