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 $26.27   5.578%   $27.7353   $27.74   $27.75   $27.70  
  Purchase #2 $239.94   4.467%   $250.6581   $250.66   $250.65   $250.70  
  Purchase #3 $175.61   3.839%   $182.3517   $182.35   $182.35   $182.40  
  Purchase #4 $197.70   5.209%   $207.9982   $208.00   $208.00   $208.00  
  Purchase #5 $107.73   6.260%   $114.4739   $114.47   $114.45   $114.50  
  Purchase #6 $241.45   5.315%   $254.2831   $254.28   $254.30   $254.30  
  Purchase #7 $159.49   13.439%   $180.9239   $180.92   $180.90   $180.90  
  7 purchase totals = $1,148.19       $1,218.4242   $1,218.42   $1,218.40   $1,218.50