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 $67.42   13.297%   $76.3848   $76.38   $76.40   $76.40  
  Purchase #2 $248.47   5.370%   $261.8128   $261.81   $261.80   $261.80  
  Purchase #3 $116.46   9.834%   $127.9127   $127.91   $127.90   $127.90  
  Purchase #4 $198.77   11.839%   $222.3024   $222.30   $222.30   $222.30  
  Purchase #5 $158.65   12.316%   $178.1893   $178.19   $178.20   $178.20  
  Purchase #6 $229.92   12.105%   $257.7518   $257.75   $257.75   $257.80  
  Purchase #7 $27.65   8.482%   $29.9953   $30.00   $30.00   $30.00  
  7 purchase totals = $1,047.34       $1,154.3491   $1,154.34   $1,154.35   $1,154.40