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 $234.28   11.708%   $261.7095   $261.71   $261.70   $261.70  
  Purchase #2 $241.77   7.818%   $260.6716   $260.67   $260.65   $260.70  
  Purchase #3 $125.89   5.652%   $133.0053   $133.01   $133.00   $133.00  
  Purchase #4 $147.89   11.238%   $164.5099   $164.51   $164.50   $164.50  
  Purchase #5 $188.35   7.342%   $202.1787   $202.18   $202.20   $202.20  
  Purchase #6 $137.93   4.334%   $143.9079   $143.91   $143.90   $143.90  
  Purchase #7 $249.66   10.661%   $276.2763   $276.28   $276.30   $276.30  
  7 purchase totals = $1,325.77       $1,442.2592   $1,442.27   $1,442.25   $1,442.30