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	$127.36	13.162%	$144.1231	$144.12	$144.10	$144.10
Purchase #2	$117.58	5.392%	$123.9199	$123.92	$123.90	$123.90
Purchase #3	$200.85	11.328%	$223.6023	$223.60	$223.60	$223.60
Purchase #4	$144.48	6.383%	$153.7022	$153.70	$153.70	$153.70
Purchase #5	$242.62	9.820%	$266.4453	$266.45	$266.45	$266.40
Purchase #6	$167.53	3.395%	$173.2176	$173.22	$173.20	$173.20
Purchase #7	$193.29	11.353%	$215.2342	$215.23	$215.25	$215.20
7 purchase totals =	$1,193.71		$1,300.2446	$1,300.24	$1,300.20	$1,300.10