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 $192.49   8.104%   $208.0894   $208.09   $208.10   $208.10  
  Purchase #2 $119.97   9.159%   $130.9581   $130.96   $130.95   $131.00  
  Purchase #3 $227.59   13.189%   $257.6068   $257.61   $257.60   $257.60  
  Purchase #4 $196.50   8.164%   $212.5423   $212.54   $212.55   $212.50  
  Purchase #5 $127.39   11.113%   $141.5469   $141.55   $141.55   $141.50  
  Purchase #6 $216.47   9.400%   $236.8182   $236.82   $236.80   $236.80  
  Purchase #7 $224.34   5.416%   $236.4903   $236.49   $236.50   $236.50  
  7 purchase totals = $1,304.75       $1,424.0520   $1,424.06   $1,424.05   $1,424.00