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 $56.74   5.677%   $59.9611   $59.96   $59.95   $60.00  
  Purchase #2 $142.68   11.832%   $159.5619   $159.56   $159.55   $159.60  
  Purchase #3 $78.48   10.253%   $86.5266   $86.53   $86.55   $86.50  
  Purchase #4 $48.74   10.269%   $53.7451   $53.75   $53.75   $53.70  
  Purchase #5 $199.87   6.683%   $213.2273   $213.23   $213.25   $213.20  
  Purchase #6 $177.95   7.418%   $191.1503   $191.15   $191.15   $191.20  
  Purchase #7 $115.50   3.728%   $119.8058   $119.81   $119.80   $119.80  
  7 purchase totals = $819.96       $883.9781   $883.99   $884.00   $884.00