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	$114.70	11.667%	$128.082	$128.08	$128.10	$128.10
Purchase #2	$85.99	8.613%	$93.3963	$93.40	$93.40	$93.40
Purchase #3	$33.42	11.744%	$37.3448	$37.34	$37.35	$37.30
Purchase #4	$102.71	8.321%	$111.2565	$111.26	$111.25	$111.30
Purchase #5	$22.58	8.839%	$24.5758	$24.58	$24.60	$24.60
Purchase #6	$154.33	12.486%	$173.5996	$173.60	$173.60	$173.60
Purchase #7	$67.33	5.163%	$70.8062	$70.81	$70.80	$70.80
7 purchase totals =	$581.06		$639.0612	$639.07	$639.10	$639.10