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 $208.83   13.545%   $237.116   $237.12   $237.10   $237.10  
  Purchase #2 $67.60   5.431%   $71.2714   $71.27   $71.25   $71.30  
  Purchase #3 $73.38   8.569%   $79.6679   $79.67   $79.65   $79.70  
  Purchase #4 $192.89   10.536%   $213.2129   $213.21   $213.20   $213.20  
  Purchase #5 $239.53   4.725%   $250.8478   $250.85   $250.85   $250.80  
  Purchase #6 $236.45   6.806%   $252.5428   $252.54   $252.55   $252.50  
  Purchase #7 $174.35   5.477%   $183.8991   $183.90   $183.90   $183.90  
  7 purchase totals = $1,193.03       $1,288.5579   $1,288.56   $1,288.50   $1,288.50