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 $209.70   11.662%   $234.1552   $234.16   $234.15   $234.20  
  Purchase #2 $139.48   6.204%   $148.1333   $148.13   $148.15   $148.10  
  Purchase #3 $110.61   3.797%   $114.8099   $114.81   $114.80   $114.80  
  Purchase #4 $42.51   12.138%   $47.6699   $47.67   $47.65   $47.70  
  Purchase #5 $47.97   8.632%   $52.1108   $52.11   $52.10   $52.10  
  Purchase #6 $115.82   5.604%   $122.3106   $122.31   $122.30   $122.30  
  Purchase #7 $216.54   11.173%   $240.734   $240.73   $240.75   $240.70  
  7 purchase totals = $882.63       $959.9237   $959.92   $959.90   $959.90