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	$92.63	7.659%	$99.7245	$99.72	$99.70	$99.70
Purchase #2	$67.63	4.592%	$70.7356	$70.74	$70.75	$70.70
Purchase #3	$156.47	6.118%	$166.0428	$166.04	$166.05	$166.00
Purchase #4	$61.42	9.451%	$67.2248	$67.22	$67.20	$67.20
Purchase #5	$60.42	10.292%	$66.6384	$66.64	$66.65	$66.60
Purchase #6	$158.42	9.183%	$172.9677	$172.97	$172.95	$173.00
Purchase #7	$167.91	13.829%	$191.1303	$191.13	$191.15	$191.10
7 purchase totals =	$764.90		$834.4641	$834.46	$834.45	$834.30