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 $60.76   13.866%   $69.185   $69.19   $69.20   $69.20  
  Purchase #2 $192.78   7.339%   $206.9281   $206.93   $206.95   $206.90  
  Purchase #3 $45.49   8.375%   $49.2998   $49.30   $49.30   $49.30  
  Purchase #4 $109.26   13.704%   $124.233   $124.23   $124.25   $124.20  
  Purchase #5 $84.34   6.851%   $90.1181   $90.12   $90.10   $90.10  
  Purchase #6 $157.41   12.411%   $176.9462   $176.95   $176.95   $176.90  
  Purchase #7 $69.46   3.556%   $71.93   $71.93   $71.95   $71.90  
  7 purchase totals = $719.50       $788.6402   $788.65   $788.70   $788.50