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 $195.58   4.225%   $203.8433   $203.84   $203.85   $203.80  
  Purchase #2 $30.88   6.861%   $32.9987   $33.00   $33.00   $33.00  
  Purchase #3 $116.70   6.839%   $124.6811   $124.68   $124.70   $124.70  
  Purchase #4 $208.30   11.666%   $232.6003   $232.60   $232.60   $232.60  
  Purchase #5 $244.25   7.308%   $262.0998   $262.10   $262.10   $262.10  
  Purchase #6 $16.53   6.462%   $17.5982   $17.60   $17.60   $17.60  
  Purchase #7 $81.53   6.577%   $86.8922   $86.89   $86.90   $86.90  
  7 purchase totals = $893.77       $960.7136   $960.71   $960.75   $960.70