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	$238.83	13.341%	$270.6923	$270.69	$270.70	$270.70
Purchase #2	$138.52	5.702%	$146.4184	$146.42	$146.40	$146.40
Purchase #3	$66.66	3.682%	$69.1144	$69.11	$69.10	$69.10
Purchase #4	$225.52	13.813%	$256.6711	$256.67	$256.65	$256.70
Purchase #5	$74.28	12.491%	$83.5583	$83.56	$83.55	$83.60
Purchase #6	$182.75	7.527%	$196.5056	$196.51	$196.50	$196.50
Purchase #7	$153.50	8.852%	$167.0878	$167.09	$167.10	$167.10
7 purchase totals =	$1,080.06		$1,190.0479	$1,190.05	$1,190.00	$1,190.10