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	$30.91	11.679%	$34.52	$34.52	$34.50	$34.50
Purchase #2	$229.94	10.151%	$253.2812	$253.28	$253.30	$253.30
Purchase #3	$236.44	7.466%	$254.0926	$254.09	$254.10	$254.10
Purchase #4	$151.73	5.179%	$159.5881	$159.59	$159.60	$159.60
Purchase #5	$69.40	3.780%	$72.0233	$72.02	$72.00	$72.00
Purchase #6	$68.25	4.127%	$71.0667	$71.07	$71.05	$71.10
Purchase #7	$38.29	8.178%	$41.4214	$41.42	$41.40	$41.40
7 purchase totals =	$824.96		$885.9933	$885.99	$885.95	$886.00