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 $239.41   9.287%   $261.644   $261.64   $261.65   $261.60  
  Purchase #2 $214.72   5.391%   $226.2956   $226.30   $226.30   $226.30  
  Purchase #3 $55.68   6.227%   $59.1472   $59.15   $59.15   $59.10  
  Purchase #4 $222.78   6.639%   $237.5704   $237.57   $237.55   $237.60  
  Purchase #5 $41.82   11.211%   $46.5084   $46.51   $46.50   $46.50  
  Purchase #6 $237.65   6.568%   $253.2589   $253.26   $253.25   $253.30  
  Purchase #7 $128.92   9.275%   $140.8773   $140.88   $140.90   $140.90  
  7 purchase totals = $1,140.98       $1,225.3018   $1,225.31   $1,225.30   $1,225.30