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	$143.35	8.351%	$155.3212	$155.32	$155.30	$155.30
Purchase #2	$116.60	4.512%	$121.861	$121.86	$121.85	$121.90
Purchase #3	$27.32	4.434%	$28.5314	$28.53	$28.55	$28.50
Purchase #4	$40.68	12.113%	$45.6076	$45.61	$45.60	$45.60
Purchase #5	$170.87	5.352%	$180.015	$180.02	$180.00	$180.00
Purchase #6	$164.92	5.128%	$173.3771	$173.38	$173.40	$173.40
Purchase #7	$124.52	12.375%	$139.9294	$139.93	$139.95	$139.90
7 purchase totals =	$788.26		$844.6427	$844.65	$844.65	$844.60