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 $182.30   6.781%   $194.6618   $194.66   $194.65   $194.70  
  Purchase #2 $95.45   10.633%   $105.5992   $105.60   $105.60   $105.60  
  Purchase #3 $135.41   6.806%   $144.626   $144.63   $144.65   $144.60  
  Purchase #4 $236.95   6.607%   $252.6053   $252.61   $252.60   $252.60  
  Purchase #5 $166.81   13.763%   $189.7681   $189.77   $189.75   $189.80  
  Purchase #6 $186.57   10.644%   $206.4285   $206.43   $206.45   $206.40  
  Purchase #7 $158.65   3.724%   $164.5581   $164.56   $164.55   $164.60  
  7 purchase totals = $1,162.14       $1,258.2470   $1,258.26   $1,258.25   $1,258.30