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	$61.83	5.370%	$65.1503	$65.15	$65.15	$65.20
Purchase #2	$153.29	12.618%	$172.6321	$172.63	$172.65	$172.60
Purchase #3	$226.54	13.250%	$256.5566	$256.56	$256.55	$256.60
Purchase #4	$67.47	4.351%	$70.4056	$70.41	$70.40	$70.40
Purchase #5	$178.60	7.151%	$191.3717	$191.37	$191.35	$191.40
Purchase #6	$223.25	8.648%	$242.5567	$242.56	$242.55	$242.60
Purchase #7	$164.27	5.312%	$172.996	$173.00	$173.00	$173.00
7 purchase totals =	$1,075.25		$1,171.6690	$1,171.68	$1,171.65	$1,171.80