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 $241.49   11.598%   $269.498   $269.50   $269.50   $269.50  
  Purchase #2 $248.88   3.236%   $256.9338   $256.93   $256.95   $256.90  
  Purchase #3 $88.48   8.129%   $95.6725   $95.67   $95.65   $95.70  
  Purchase #4 $86.56   6.309%   $92.0211   $92.02   $92.00   $92.00  
  Purchase #5 $114.58   7.258%   $122.8962   $122.90   $122.90   $122.90  
  Purchase #6 $225.57   12.851%   $254.558   $254.56   $254.55   $254.60  
  Purchase #7 $69.90   8.810%   $76.0582   $76.06   $76.05   $76.10  
  7 purchase totals = $1,075.46       $1,167.6378   $1,167.64   $1,167.60   $1,167.70