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 $49.88   11.457%   $55.5948   $55.59   $55.60   $55.60  
  Purchase #2 $147.61   8.674%   $160.4137   $160.41   $160.40   $160.40  
  Purchase #3 $242.66   4.169%   $252.7765   $252.78   $252.80   $252.80  
  Purchase #4 $248.85   9.347%   $272.11   $272.11   $272.10   $272.10  
  Purchase #5 $62.63   3.857%   $65.0456   $65.05   $65.05   $65.00  
  Purchase #6 $136.38   11.519%   $152.0896   $152.09   $152.10   $152.10  
  Purchase #7 $89.81   5.340%   $94.6059   $94.61   $94.60   $94.60  
  7 purchase totals = $977.82       $1,052.6361   $1,052.64   $1,052.65   $1,052.60