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 $246.36   7.661%   $265.2336   $265.23   $265.25   $265.20  
  Purchase #2 $218.47   4.311%   $227.8882   $227.89   $227.90   $227.90  
  Purchase #3 $244.35   7.516%   $262.7153   $262.72   $262.70   $262.70  
  Purchase #4 $226.28   10.241%   $249.4533   $249.45   $249.45   $249.50  
  Purchase #5 $176.97   3.381%   $182.9534   $182.95   $182.95   $183.00  
  Purchase #6 $92.42   6.772%   $98.6787   $98.68   $98.70   $98.70  
  Purchase #7 $161.99   5.505%   $170.9075   $170.91   $170.90   $170.90  
  7 purchase totals = $1,366.84       $1,457.8300   $1,457.83   $1,457.85   $1,457.90