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 $69.67   5.792%   $73.7053   $73.71   $73.70   $73.70  
  Purchase #2 $192.53   7.838%   $207.6205   $207.62   $207.60   $207.60  
  Purchase #3 $78.48   10.683%   $86.864   $86.86   $86.85   $86.90  
  Purchase #4 $95.92   11.784%   $107.2232   $107.22   $107.20   $107.20  
  Purchase #5 $237.73   10.742%   $263.267   $263.27   $263.25   $263.30  
  Purchase #6 $124.56   4.806%   $130.5464   $130.55   $130.55   $130.50  
  Purchase #7 $53.51   12.609%   $60.2571   $60.26   $60.25   $60.30  
  7 purchase totals = $852.40       $929.4835   $929.49   $929.40   $929.50