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 $222.53   7.536%   $239.2999   $239.30   $239.30   $239.30  
  Purchase #2 $195.93   10.586%   $216.6711   $216.67   $216.65   $216.70  
  Purchase #3 $235.81   6.407%   $250.9183   $250.92   $250.90   $250.90  
  Purchase #4 $115.96   5.624%   $122.4816   $122.48   $122.50   $122.50  
  Purchase #5 $84.70   9.368%   $92.6347   $92.63   $92.65   $92.60  
  Purchase #6 $44.49   7.829%   $47.9731   $47.97   $47.95   $48.00  
  Purchase #7 $195.93   9.214%   $213.983   $213.98   $214.00   $214.00  
  7 purchase totals = $1,095.35       $1,183.9617   $1,183.95   $1,183.95   $1,184.00