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 $25.72   5.744%   $27.1974   $27.20   $27.20   $27.20  
  Purchase #2 $206.49   8.484%   $224.0086   $224.01   $224.00   $224.00  
  Purchase #3 $39.64   6.857%   $42.3581   $42.36   $42.35   $42.40  
  Purchase #4 $95.63   4.163%   $99.6111   $99.61   $99.60   $99.60  
  Purchase #5 $96.95   11.543%   $108.1409   $108.14   $108.15   $108.10  
  Purchase #6 $136.64   12.248%   $153.3757   $153.38   $153.40   $153.40  
  Purchase #7 $56.96   10.621%   $63.0097   $63.01   $63.00   $63.00  
  7 purchase totals = $658.03       $717.7015   $717.71   $717.70   $717.70