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 $124.43   13.683%   $141.4558   $141.46   $141.45   $141.50  
  Purchase #2 $100.55   8.646%   $109.2436   $109.24   $109.25   $109.20  
  Purchase #3 $49.55   13.874%   $56.4246   $56.42   $56.40   $56.40  
  Purchase #4 $234.82   6.447%   $249.9588   $249.96   $249.95   $250.00  
  Purchase #5 $68.46   4.484%   $71.5297   $71.53   $71.55   $71.50  
  Purchase #6 $11.35   5.525%   $11.9771   $11.98   $12.00   $12.00  
  Purchase #7 $76.92   12.253%   $86.345   $86.35   $86.35   $86.30  
  7 purchase totals = $666.08       $726.9346   $726.94   $726.95   $726.90