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	$235.83	3.415%	$243.8836	$243.88	$243.90	$243.90
Purchase #2	$120.66	5.849%	$127.7174	$127.72	$127.70	$127.70
Purchase #3	$188.38	4.413%	$196.6932	$196.69	$196.70	$196.70
Purchase #4	$230.37	6.106%	$244.4364	$244.44	$244.45	$244.40
Purchase #5	$16.78	10.737%	$18.5817	$18.58	$18.60	$18.60
Purchase #6	$213.73	5.749%	$226.0173	$226.02	$226.00	$226.00
Purchase #7	$37.73	11.656%	$42.1278	$42.13	$42.15	$42.10
7 purchase totals =	$1,043.48		$1,099.4574	$1,099.46	$1,099.50	$1,099.40