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 $207.43   8.258%   $224.5596   $224.56   $224.55   $224.60  
  Purchase #2 $226.56   3.553%   $234.6097   $234.61   $234.60   $234.60  
  Purchase #3 $44.50   5.214%   $46.8202   $46.82   $46.80   $46.80  
  Purchase #4 $190.75   12.274%   $214.1627   $214.16   $214.15   $214.20  
  Purchase #5 $174.67   10.469%   $192.9562   $192.96   $192.95   $193.00  
  Purchase #6 $241.51   8.142%   $261.1737   $261.17   $261.15   $261.20  
  Purchase #7 $201.57   12.774%   $227.3186   $227.32   $227.30   $227.30  
  7 purchase totals = $1,286.99       $1,401.6007   $1,401.60   $1,401.50   $1,401.70