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 $138.86   3.873%   $144.238   $144.24   $144.25   $144.20  
  Purchase #2 $228.75   7.863%   $246.7366   $246.74   $246.75   $246.70  
  Purchase #3 $233.81   6.525%   $249.0661   $249.07   $249.05   $249.10  
  Purchase #4 $176.32   6.808%   $188.3239   $188.32   $188.30   $188.30  
  Purchase #5 $26.60   3.139%   $27.435   $27.44   $27.45   $27.40  
  Purchase #6 $178.77   6.373%   $190.163   $190.16   $190.15   $190.20  
  Purchase #7 $140.63   11.724%   $157.1175   $157.12   $157.10   $157.10  
  7 purchase totals = $1,123.74       $1,203.0801   $1,203.09   $1,203.05   $1,203.00