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 $57.71   5.205%   $60.7138   $60.71   $60.70   $60.70  
  Purchase #2 $115.64   7.554%   $124.3754   $124.38   $124.40   $124.40  
  Purchase #3 $206.88   3.212%   $213.525   $213.53   $213.55   $213.50  
  Purchase #4 $149.28   7.761%   $160.8656   $160.87   $160.85   $160.90  
  Purchase #5 $63.41   10.656%   $70.167   $70.17   $70.15   $70.20  
  Purchase #6 $51.25   11.127%   $56.9526   $56.95   $56.95   $57.00  
  Purchase #7 $82.73   8.796%   $90.0069   $90.01   $90.00   $90.00  
  7 purchase totals = $726.90       $776.6063   $776.62   $776.60   $776.70