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	$125.44	8.845%	$136.5352	$136.54	$136.55	$136.50
Purchase #2	$112.36	5.755%	$118.8263	$118.83	$118.85	$118.80
Purchase #3	$162.65	6.735%	$173.6045	$173.60	$173.60	$173.60
Purchase #4	$177.95	3.658%	$184.4594	$184.46	$184.45	$184.50
Purchase #5	$158.47	8.636%	$172.1555	$172.16	$172.15	$172.20
Purchase #6	$153.80	13.671%	$174.826	$174.83	$174.85	$174.80
Purchase #7	$241.29	3.767%	$250.3794	$250.38	$250.40	$250.40
7 purchase totals =	$1,131.96		$1,210.7863	$1,210.80	$1,210.85	$1,210.80