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	$239.70	12.416%	$269.4612	$269.46	$269.45	$269.50
Purchase #2	$111.37	6.125%	$118.1914	$118.19	$118.20	$118.20
Purchase #3	$50.38	10.867%	$55.8548	$55.85	$55.85	$55.90
Purchase #4	$216.84	6.289%	$230.4771	$230.48	$230.50	$230.50
Purchase #5	$215.28	10.773%	$238.4721	$238.47	$238.45	$238.50
Purchase #6	$39.82	6.548%	$42.4274	$42.43	$42.45	$42.40
Purchase #7	$158.40	8.806%	$172.3487	$172.35	$172.35	$172.30
7 purchase totals =	$1,031.79		$1,127.2327	$1,127.23	$1,127.25	$1,127.30