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 $249.46   5.151%   $262.3097   $262.31   $262.30   $262.30  
  Purchase #2 $125.59   8.691%   $136.505   $136.51   $136.50   $136.50  
  Purchase #3 $78.93   7.160%   $84.5814   $84.58   $84.60   $84.60  
  Purchase #4 $69.34   5.624%   $73.2397   $73.24   $73.25   $73.20  
  Purchase #5 $241.86   8.241%   $261.7917   $261.79   $261.80   $261.80  
  Purchase #6 $162.42   9.805%   $178.3453   $178.35   $178.35   $178.30  
  Purchase #7 $26.37   5.734%   $27.8821   $27.88   $27.90   $27.90  
  7 purchase totals = $953.97       $1,024.6549   $1,024.66   $1,024.70   $1,024.60