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	$162.87	10.647%	$180.2108	$180.21	$180.20	$180.20
Purchase #2	$88.27	3.167%	$91.0655	$91.07	$91.05	$91.10
Purchase #3	$95.27	8.551%	$103.4165	$103.42	$103.40	$103.40
Purchase #4	$139.90	9.283%	$152.8869	$152.89	$152.90	$152.90
Purchase #5	$141.81	11.823%	$158.5762	$158.58	$158.60	$158.60
Purchase #6	$123.52	8.836%	$134.4342	$134.43	$134.45	$134.40
Purchase #7	$172.68	4.326%	$180.1501	$180.15	$180.15	$180.20
7 purchase totals =	$924.32		$1,000.7402	$1,000.75	$1,000.75	$1,000.80