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 $248.58   5.217%   $261.5484   $261.55   $261.55   $261.50  
  Purchase #2 $74.79   9.337%   $81.7731   $81.77   $81.75   $81.80  
  Purchase #3 $234.41   6.649%   $249.9959   $250.00   $250.00   $250.00  
  Purchase #4 $110.73   3.157%   $114.2257   $114.23   $114.25   $114.20  
  Purchase #5 $134.74   8.357%   $146.0002   $146.00   $146.00   $146.00  
  Purchase #6 $103.83   4.352%   $108.3487   $108.35   $108.35   $108.30  
  Purchase #7 $84.81   4.576%   $88.6909   $88.69   $88.70   $88.70  
  7 purchase totals = $991.89       $1,050.5829   $1,050.59   $1,050.60   $1,050.50