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 $29.44   11.189%   $32.734   $32.73   $32.75   $32.70  
  Purchase #2 $195.62   5.522%   $206.4221   $206.42   $206.40   $206.40  
  Purchase #3 $164.81   10.115%   $181.4805   $181.48   $181.50   $181.50  
  Purchase #4 $219.83   13.251%   $248.9597   $248.96   $248.95   $249.00  
  Purchase #5 $54.26   7.723%   $58.4505   $58.45   $58.45   $58.50  
  Purchase #6 $126.28   13.508%   $143.3379   $143.34   $143.35   $143.30  
  Purchase #7 $133.75   4.631%   $139.944   $139.94   $139.95   $139.90  
  7 purchase totals = $923.99       $1,011.3287   $1,011.32   $1,011.35   $1,011.30