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	$237.76	5.265%	$250.2781	$250.28	$250.30	$250.30
Purchase #2	$146.93	10.243%	$161.98	$161.98	$162.00	$162.00
Purchase #3	$232.92	13.375%	$264.0731	$264.07	$264.05	$264.10
Purchase #4	$167.29	3.397%	$172.9728	$172.97	$172.95	$173.00
Purchase #5	$11.83	5.574%	$12.4894	$12.49	$12.50	$12.50
Purchase #6	$121.52	4.678%	$127.2047	$127.20	$127.20	$127.20
Purchase #7	$79.78	12.309%	$89.6001	$89.60	$89.60	$89.60
7 purchase totals =	$998.03		$1,078.5982	$1,078.59	$1,078.60	$1,078.70