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 $250.69   6.691%   $267.4637   $267.46   $267.45   $267.50  
  Purchase #2 $5.69   4.197%   $5.9288   $5.93   $5.95   $5.90  
  Purchase #3 $31.46   8.138%   $34.0202   $34.02   $34.00   $34.00  
  Purchase #4 $86.62   6.454%   $92.2105   $92.21   $92.20   $92.20  
  Purchase #5 $221.42   5.643%   $233.9147   $233.91   $233.90   $233.90  
  Purchase #6 $6.96   3.402%   $7.1968   $7.20   $7.20   $7.20  
  Purchase #7 $79.90   7.657%   $86.0179   $86.02   $86.00   $86.00  
  7 purchase totals = $682.74       $726.7526   $726.75   $726.70   $726.70