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	$230.82	9.218%	$252.097	$252.10	$252.10	$252.10
Purchase #2	$249.55	6.826%	$266.5843	$266.58	$266.60	$266.60
Purchase #3	$30.73	5.452%	$32.4054	$32.41	$32.40	$32.40
Purchase #4	$118.49	13.190%	$134.1188	$134.12	$134.10	$134.10
Purchase #5	$89.70	13.574%	$101.8759	$101.88	$101.90	$101.90
Purchase #6	$59.68	3.443%	$61.7348	$61.73	$61.75	$61.70
Purchase #7	$146.50	4.781%	$153.5042	$153.50	$153.50	$153.50
7 purchase totals =	$925.47		$1,002.3204	$1,002.32	$1,002.35	$1,002.30