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 $242.52   7.642%   $261.0534   $261.05   $261.05   $261.10  
  Purchase #2 $213.88   12.423%   $240.4503   $240.45   $240.45   $240.50  
  Purchase #3 $18.65   4.854%   $19.5553   $19.56   $19.55   $19.60  
  Purchase #4 $30.84   11.102%   $34.2639   $34.26   $34.25   $34.30  
  Purchase #5 $115.40   8.458%   $125.1605   $125.16   $125.15   $125.20  
  Purchase #6 $148.32   6.757%   $158.342   $158.34   $158.35   $158.30  
  Purchase #7 $216.38   4.849%   $226.8723   $226.87   $226.85   $226.90  
  7 purchase totals = $985.99       $1,065.6977   $1,065.69   $1,065.65   $1,065.90