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	$80.90	13.378%	$91.7228	$91.72	$91.70	$91.70
Purchase #2	$108.88	5.276%	$114.6245	$114.62	$114.60	$114.60
Purchase #3	$107.63	10.157%	$118.562	$118.56	$118.55	$118.60
Purchase #4	$48.41	4.498%	$50.5875	$50.59	$50.60	$50.60
Purchase #5	$100.37	10.590%	$110.9992	$111.00	$111.00	$111.00
Purchase #6	$100.78	4.379%	$105.1932	$105.19	$105.20	$105.20
Purchase #7	$41.73	8.480%	$45.2687	$45.27	$45.25	$45.30
7 purchase totals =	$588.70		$636.9579	$636.95	$636.90	$637.00