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 $236.26   10.602%   $261.3083   $261.31   $261.30   $261.30  
  Purchase #2 $13.61   3.749%   $14.1202   $14.12   $14.10   $14.10  
  Purchase #3 $166.92   6.761%   $178.2055   $178.21   $178.20   $178.20  
  Purchase #4 $219.82   13.105%   $248.6274   $248.63   $248.65   $248.60  
  Purchase #5 $8.90   7.125%   $9.5341   $9.53   $9.55   $9.50  
  Purchase #6 $230.65   4.403%   $240.8055   $240.81   $240.80   $240.80  
  Purchase #7 $63.76   5.138%   $67.036   $67.04   $67.05   $67.00  
  7 purchase totals = $939.92       $1,019.6370   $1,019.65   $1,019.65   $1,019.50