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 $203.41   11.109%   $226.0068   $226.01   $226.00   $226.00  
  Purchase #2 $47.92   4.410%   $50.0333   $50.03   $50.05   $50.00  
  Purchase #3 $111.76   11.871%   $125.027   $125.03   $125.05   $125.00  
  Purchase #4 $115.64   5.813%   $122.3622   $122.36   $122.35   $122.40  
  Purchase #5 $175.89   13.311%   $199.3027   $199.30   $199.30   $199.30  
  Purchase #6 $245.49   6.420%   $261.2505   $261.25   $261.25   $261.30  
  Purchase #7 $27.91   4.538%   $29.1766   $29.18   $29.20   $29.20  
  7 purchase totals = $928.02       $1,013.1591   $1,013.16   $1,013.20   $1,013.20