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 $141.25   12.652%   $159.121   $159.12   $159.10   $159.10  
  Purchase #2 $224.64   10.243%   $247.6499   $247.65   $247.65   $247.60  
  Purchase #3 $169.59   4.130%   $176.5941   $176.59   $176.60   $176.60  
  Purchase #4 $64.63   8.745%   $70.2819   $70.28   $70.30   $70.30  
  Purchase #5 $40.81   4.758%   $42.7517   $42.75   $42.75   $42.80  
  Purchase #6 $54.87   12.252%   $61.5927   $61.59   $61.60   $61.60  
  Purchase #7 $64.76   6.786%   $69.1546   $69.15   $69.15   $69.20  
  7 purchase totals = $760.55       $827.1459   $827.13   $827.15   $827.20