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 $249.71   7.117%   $267.4819   $267.48   $267.50   $267.50  
  Purchase #2 $110.81   3.461%   $114.6451   $114.65   $114.65   $114.60  
  Purchase #3 $248.43   8.524%   $269.6062   $269.61   $269.60   $269.60  
  Purchase #4 $232.64   3.205%   $240.0961   $240.10   $240.10   $240.10  
  Purchase #5 $195.33   11.197%   $217.2011   $217.20   $217.20   $217.20  
  Purchase #6 $57.44   5.439%   $60.5642   $60.56   $60.55   $60.60  
  Purchase #7 $89.36   4.115%   $93.0372   $93.04   $93.05   $93.00  
  7 purchase totals = $1,183.72       $1,262.6318   $1,262.64   $1,262.65   $1,262.60