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 $249.57   13.124%   $282.3236   $282.32   $282.30   $282.30  
  Purchase #2 $195.92   10.785%   $217.05   $217.05   $217.05   $217.10  
  Purchase #3 $248.69   3.873%   $258.3218   $258.32   $258.30   $258.30  
  Purchase #4 $250.78   13.121%   $283.6848   $283.68   $283.70   $283.70  
  Purchase #5 $149.65   9.726%   $164.205   $164.21   $164.20   $164.20  
  Purchase #6 $208.39   3.508%   $215.7003   $215.70   $215.70   $215.70  
  Purchase #7 $239.44   6.509%   $255.0251   $255.03   $255.05   $255.00  
  7 purchase totals = $1,542.44       $1,676.3106   $1,676.31   $1,676.30   $1,676.30