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 $55.87   9.617%   $61.243   $61.24   $61.25   $61.20  
  Purchase #2 $169.27   8.147%   $183.0604   $183.06   $183.05   $183.10  
  Purchase #3 $139.47   12.446%   $156.8284   $156.83   $156.85   $156.80  
  Purchase #4 $124.84   10.868%   $138.4076   $138.41   $138.40   $138.40  
  Purchase #5 $156.92   12.181%   $176.0344   $176.03   $176.05   $176.00  
  Purchase #6 $52.71   5.302%   $55.5047   $55.50   $55.50   $55.50  
  Purchase #7 $116.51   8.780%   $126.7396   $126.74   $126.75   $126.70  
  7 purchase totals = $815.59       $897.8181   $897.81   $897.85   $897.70