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	$31.33	3.540%	$32.4391	$32.44	$32.45	$32.40
Purchase #2	$217.65	5.762%	$230.191	$230.19	$230.20	$230.20
Purchase #3	$79.29	12.810%	$89.447	$89.45	$89.45	$89.40
Purchase #4	$233.64	3.152%	$241.0043	$241.00	$241.00	$241.00
Purchase #5	$74.73	4.583%	$78.1549	$78.15	$78.15	$78.20
Purchase #6	$130.60	6.669%	$139.3097	$139.31	$139.30	$139.30
Purchase #7	$38.44	11.485%	$42.8548	$42.85	$42.85	$42.90
7 purchase totals =	$805.68		$853.4008	$853.39	$853.40	$853.40