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 $32.29   3.628%   $33.4615   $33.46   $33.45   $33.50  
  Purchase #2 $177.51   10.839%   $196.7503   $196.75   $196.75   $196.80  
  Purchase #3 $200.70   6.710%   $214.167   $214.17   $214.15   $214.20  
  Purchase #4 $136.66   13.197%   $154.695   $154.70   $154.70   $154.70  
  Purchase #5 $30.60   8.185%   $33.1046   $33.10   $33.10   $33.10  
  Purchase #6 $122.46   4.755%   $128.283   $128.28   $128.30   $128.30  
  Purchase #7 $65.30   12.170%   $73.247   $73.25   $73.25   $73.20  
  7 purchase totals = $765.52       $833.7084   $833.71   $833.70   $833.80