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 $220.83   8.131%   $238.7857   $238.79   $238.80   $238.80  
  Purchase #2 $82.90   11.737%   $92.63   $92.63   $92.65   $92.60  
  Purchase #3 $227.81   12.405%   $256.0698   $256.07   $256.05   $256.10  
  Purchase #4 $200.61   8.527%   $217.716   $217.72   $217.70   $217.70  
  Purchase #5 $228.74   7.219%   $245.2527   $245.25   $245.25   $245.30  
  Purchase #6 $249.60   6.744%   $266.433   $266.43   $266.45   $266.40  
  Purchase #7 $137.84   10.240%   $151.9548   $151.95   $151.95   $152.00  
  7 purchase totals = $1,348.33       $1,468.8420   $1,468.84   $1,468.85   $1,468.90