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 $108.61   8.333%   $117.6605   $117.66   $117.65   $117.70  
  Purchase #2 $183.85   12.250%   $206.3716   $206.37   $206.35   $206.40  
  Purchase #3 $157.42   10.416%   $173.8169   $173.82   $173.80   $173.80  
  Purchase #4 $56.63   12.382%   $63.6419   $63.64   $63.65   $63.60  
  Purchase #5 $220.82   6.689%   $235.5906   $235.59   $235.60   $235.60  
  Purchase #6 $114.66   3.867%   $119.0939   $119.09   $119.10   $119.10  
  Purchase #7 $57.94   4.436%   $60.5102   $60.51   $60.50   $60.50  
  7 purchase totals = $899.93       $976.6856   $976.68   $976.65   $976.70