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 $213.38   13.241%   $241.6336   $241.63   $241.65   $241.60  
  Purchase #2 $32.54   4.241%   $33.92   $33.92   $33.90   $33.90  
  Purchase #3 $63.36   12.163%   $71.0665   $71.07   $71.05   $71.10  
  Purchase #4 $219.62   3.733%   $227.8184   $227.82   $227.80   $227.80  
  Purchase #5 $73.55   10.639%   $81.375   $81.38   $81.40   $81.40  
  Purchase #6 $78.99   9.624%   $86.592   $86.59   $86.60   $86.60  
  Purchase #7 $215.37   6.209%   $228.7423   $228.74   $228.75   $228.70  
  7 purchase totals = $896.81       $971.1478   $971.15   $971.15   $971.10