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 $242.62   11.266%   $269.9536   $269.95   $269.95   $270.00  
  Purchase #2 $35.83   6.559%   $38.1801   $38.18   $38.20   $38.20  
  Purchase #3 $23.99   9.593%   $26.2914   $26.29   $26.30   $26.30  
  Purchase #4 $50.46   7.758%   $54.3747   $54.37   $54.35   $54.40  
  Purchase #5 $34.68   8.470%   $37.6174   $37.62   $37.60   $37.60  
  Purchase #6 $222.98   9.738%   $244.6938   $244.69   $244.70   $244.70  
  Purchase #7 $83.66   12.843%   $94.4045   $94.40   $94.40   $94.40  
  7 purchase totals = $694.22       $765.5155   $765.50   $765.50   $765.60