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 $88.58   10.713%   $98.0696   $98.07   $98.05   $98.10  
  Purchase #2 $70.95   4.135%   $73.8838   $73.88   $73.90   $73.90  
  Purchase #3 $65.99   6.615%   $70.3552   $70.36   $70.35   $70.40  
  Purchase #4 $249.81   12.247%   $280.4042   $280.40   $280.40   $280.40  
  Purchase #5 $208.71   9.127%   $227.759   $227.76   $227.75   $227.80  
  Purchase #6 $182.75   3.710%   $189.53   $189.53   $189.55   $189.50  
  Purchase #7 $130.49   11.239%   $145.1558   $145.16   $145.15   $145.20  
  7 purchase totals = $997.28       $1,085.1576   $1,085.16   $1,085.15   $1,085.30