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	$75.79	9.867%	$83.2682	$83.27	$83.25	$83.30
Purchase #2	$90.29	13.172%	$102.183	$102.18	$102.20	$102.20
Purchase #3	$160.86	7.733%	$173.2993	$173.30	$173.30	$173.30
Purchase #4	$206.53	10.640%	$228.5048	$228.50	$228.50	$228.50
Purchase #5	$168.71	5.852%	$178.5829	$178.58	$178.60	$178.60
Purchase #6	$45.39	11.509%	$50.6139	$50.61	$50.60	$50.60
Purchase #7	$85.44	6.255%	$90.7843	$90.78	$90.80	$90.80
7 purchase totals =	$833.01		$907.2364	$907.22	$907.25	$907.30