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	$93.78	12.359%	$105.3703	$105.37	$105.35	$105.40
Purchase #2	$213.34	4.572%	$223.0939	$223.09	$223.10	$223.10
Purchase #3	$18.81	6.380%	$20.0101	$20.01	$20.00	$20.00
Purchase #4	$21.83	10.260%	$24.0698	$24.07	$24.05	$24.10
Purchase #5	$157.67	10.269%	$173.8611	$173.86	$173.85	$173.90
Purchase #6	$19.26	6.859%	$20.581	$20.58	$20.60	$20.60
Purchase #7	$114.42	10.312%	$126.219	$126.22	$126.20	$126.20
7 purchase totals =	$639.11		$693.2052	$693.20	$693.15	$693.30