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	$45.42	6.384%	$48.3196	$48.32	$48.30	$48.30
Purchase #2	$35.75	11.261%	$39.7758	$39.78	$39.80	$39.80
Purchase #3	$132.69	6.699%	$141.5789	$141.58	$141.60	$141.60
Purchase #4	$31.70	4.569%	$33.1484	$33.15	$33.15	$33.10
Purchase #5	$36.87	11.324%	$41.0452	$41.05	$41.05	$41.00
Purchase #6	$228.92	13.326%	$259.4259	$259.43	$259.45	$259.40
Purchase #7	$118.72	7.387%	$127.4898	$127.49	$127.50	$127.50
7 purchase totals =	$630.07		$690.7836	$690.80	$690.85	$690.70