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 $223.63   7.777%   $241.0217   $241.02   $241.00   $241.00  
  Purchase #2 $132.48   8.207%   $143.3526   $143.35   $143.35   $143.40  
  Purchase #3 $195.44   6.788%   $208.7065   $208.71   $208.70   $208.70  
  Purchase #4 $75.91   4.848%   $79.5901   $79.59   $79.60   $79.60  
  Purchase #5 $72.75   7.845%   $78.4572   $78.46   $78.45   $78.50  
  Purchase #6 $140.28   3.153%   $144.703   $144.70   $144.70   $144.70  
  Purchase #7 $194.80   8.663%   $211.6755   $211.68   $211.70   $211.70  
  7 purchase totals = $1,035.29       $1,107.5066   $1,107.51   $1,107.50   $1,107.60