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	$131.73	5.622%	$139.1359	$139.14	$139.15	$139.10
Purchase #2	$139.37	5.191%	$146.6047	$146.60	$146.60	$146.60
Purchase #3	$230.56	6.397%	$245.3089	$245.31	$245.30	$245.30
Purchase #4	$54.45	12.466%	$61.2377	$61.24	$61.25	$61.20
Purchase #5	$78.80	3.403%	$81.4816	$81.48	$81.50	$81.50
Purchase #6	$161.90	10.533%	$178.9529	$178.95	$178.95	$179.00
Purchase #7	$59.75	3.189%	$61.6554	$61.66	$61.65	$61.70
7 purchase totals =	$856.56		$914.3771	$914.38	$914.40	$914.40