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	$37.88	5.156%	$39.8331	$39.83	$39.85	$39.80
Purchase #2	$29.30	8.643%	$31.8324	$31.83	$31.85	$31.80
Purchase #3	$113.77	4.847%	$119.2844	$119.28	$119.30	$119.30
Purchase #4	$230.51	11.456%	$256.9172	$256.92	$256.90	$256.90
Purchase #5	$167.66	12.183%	$188.086	$188.09	$188.10	$188.10
Purchase #6	$34.72	6.781%	$37.0744	$37.07	$37.05	$37.10
Purchase #7	$52.25	4.157%	$54.422	$54.42	$54.40	$54.40
7 purchase totals =	$666.09		$727.4495	$727.44	$727.45	$727.40