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 $248.65   3.742%   $257.9545   $257.95   $257.95   $258.00  
  Purchase #2 $242.60   11.566%   $270.6591   $270.66   $270.65   $270.70  
  Purchase #3 $27.25   6.262%   $28.9564   $28.96   $28.95   $29.00  
  Purchase #4 $236.68   10.466%   $261.4509   $261.45   $261.45   $261.50  
  Purchase #5 $218.60   9.549%   $239.4741   $239.47   $239.45   $239.50  
  Purchase #6 $57.81   13.489%   $65.608   $65.61   $65.60   $65.60  
  Purchase #7 $191.38   13.491%   $217.1991   $217.20   $217.20   $217.20  
  7 purchase totals = $1,222.97       $1,341.3021   $1,341.30   $1,341.25   $1,341.50