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 $218.74   5.493%   $230.7554   $230.76   $230.75   $230.80  
  Purchase #2 $105.44   10.354%   $116.3573   $116.36   $116.35   $116.40  
  Purchase #3 $223.55   9.873%   $245.6211   $245.62   $245.60   $245.60  
  Purchase #4 $249.35   5.284%   $262.5257   $262.53   $262.55   $262.50  
  Purchase #5 $217.85   8.364%   $236.071   $236.07   $236.05   $236.10  
  Purchase #6 $94.41   11.615%   $105.3757   $105.38   $105.40   $105.40  
  Purchase #7 $128.35   9.708%   $140.8102   $140.81   $140.80   $140.80  
  7 purchase totals = $1,237.69       $1,337.5164   $1,337.53   $1,337.50   $1,337.60