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 $55.82   9.134%   $60.9186   $60.92   $60.90   $60.90  
  Purchase #2 $221.69   8.554%   $240.6534   $240.65   $240.65   $240.70  
  Purchase #3 $66.74   8.685%   $72.5364   $72.54   $72.55   $72.50  
  Purchase #4 $195.39   11.179%   $217.2326   $217.23   $217.25   $217.20  
  Purchase #5 $243.99   6.436%   $259.6932   $259.69   $259.70   $259.70  
  Purchase #6 $249.99   4.720%   $261.7895   $261.79   $261.80   $261.80  
  Purchase #7 $113.43   3.684%   $117.6088   $117.61   $117.60   $117.60  
  7 purchase totals = $1,147.05       $1,230.4325   $1,230.43   $1,230.45   $1,230.40