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 $244.50   6.636%   $260.725   $260.73   $260.75   $260.70  
  Purchase #2 $96.68   8.714%   $105.1047   $105.10   $105.10   $105.10  
  Purchase #3 $65.45   8.329%   $70.9013   $70.90   $70.90   $70.90  
  Purchase #4 $144.28   9.767%   $158.3718   $158.37   $158.35   $158.40  
  Purchase #5 $242.75   10.838%   $269.0592   $269.06   $269.05   $269.10  
  Purchase #6 $65.71   13.268%   $74.4284   $74.43   $74.45   $74.40  
  Purchase #7 $11.44   5.175%   $12.032   $12.03   $12.05   $12.00  
  7 purchase totals = $870.81       $950.6224   $950.62   $950.65   $950.60