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 $208.35   4.793%   $218.3362   $218.34   $218.35   $218.30  
  Purchase #2 $206.61   5.706%   $218.3992   $218.40   $218.40   $218.40  
  Purchase #3 $226.27   12.698%   $255.0018   $255.00   $255.00   $255.00  
  Purchase #4 $41.87   12.346%   $47.0393   $47.04   $47.05   $47.00  
  Purchase #5 $115.68   6.834%   $123.5856   $123.59   $123.60   $123.60  
  Purchase #6 $191.36   9.213%   $208.99   $208.99   $209.00   $209.00  
  Purchase #7 $132.39   9.676%   $145.2001   $145.20   $145.20   $145.20  
  7 purchase totals = $1,122.53       $1,216.5522   $1,216.56   $1,216.60   $1,216.50