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	$114.32	3.246%	$118.0308	$118.03	$118.05	$118.00
Purchase #2	$50.83	12.715%	$57.293	$57.29	$57.30	$57.30
Purchase #3	$244.89	4.240%	$255.2733	$255.27	$255.25	$255.30
Purchase #4	$66.45	6.342%	$70.6643	$70.66	$70.65	$70.70
Purchase #5	$171.70	7.115%	$183.9165	$183.92	$183.90	$183.90
Purchase #6	$214.40	7.449%	$230.3707	$230.37	$230.35	$230.40
Purchase #7	$126.89	11.663%	$141.6892	$141.69	$141.70	$141.70
7 purchase totals =	$989.48		$1,057.2378	$1,057.23	$1,057.20	$1,057.30