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 $195.98   13.400%   $222.2413   $222.24   $222.25   $222.20  
  Purchase #2 $174.82   5.246%   $183.9911   $183.99   $184.00   $184.00  
  Purchase #3 $30.64   6.309%   $32.5731   $32.57   $32.55   $32.60  
  Purchase #4 $237.34   4.867%   $248.8913   $248.89   $248.90   $248.90  
  Purchase #5 $71.95   8.470%   $78.0442   $78.04   $78.05   $78.00  
  Purchase #6 $246.35   12.662%   $277.5428   $277.54   $277.55   $277.50  
  Purchase #7 $67.89   12.283%   $76.2289   $76.23   $76.25   $76.20  
  7 purchase totals = $1,024.97       $1,119.5127   $1,119.50   $1,119.55   $1,119.40