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 $232.28   11.432%   $258.8342   $258.83   $258.85   $258.80  
  Purchase #2 $130.75   10.382%   $144.3245   $144.32   $144.30   $144.30  
  Purchase #3 $16.95   8.865%   $18.4526   $18.45   $18.45   $18.50  
  Purchase #4 $227.41   9.792%   $249.678   $249.68   $249.70   $249.70  
  Purchase #5 $114.87   6.466%   $122.2975   $122.30   $122.30   $122.30  
  Purchase #6 $169.75   10.138%   $186.9593   $186.96   $186.95   $187.00  
  Purchase #7 $85.62   6.560%   $91.2367   $91.24   $91.25   $91.20  
  7 purchase totals = $977.63       $1,071.7828   $1,071.78   $1,071.80   $1,071.80