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	$248.94	12.365%	$279.7214	$279.72	$279.70	$279.70
Purchase #2	$22.78	10.673%	$25.2113	$25.21	$25.20	$25.20
Purchase #3	$200.91	11.203%	$223.4179	$223.42	$223.40	$223.40
Purchase #4	$128.63	13.874%	$146.4761	$146.48	$146.50	$146.50
Purchase #5	$111.69	13.721%	$127.015	$127.02	$127.00	$127.00
Purchase #6	$73.76	10.159%	$81.2533	$81.25	$81.25	$81.30
Purchase #7	$103.75	8.536%	$112.6061	$112.61	$112.60	$112.60
7 purchase totals =	$890.46		$995.7011	$995.71	$995.65	$995.70