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	$21.28	3.622%	$22.0508	$22.05	$22.05	$22.10
Purchase #2	$105.34	5.569%	$111.2064	$111.21	$111.20	$111.20
Purchase #3	$111.51	3.475%	$115.385	$115.39	$115.40	$115.40
Purchase #4	$110.39	12.257%	$123.9205	$123.92	$123.90	$123.90
Purchase #5	$244.28	11.154%	$271.527	$271.53	$271.55	$271.50
Purchase #6	$224.95	13.662%	$255.6827	$255.68	$255.70	$255.70
Purchase #7	$133.83	8.333%	$144.9821	$144.98	$145.00	$145.00
7 purchase totals =	$951.58		$1,044.7545	$1,044.76	$1,044.80	$1,044.80