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	$173.69	5.521%	$183.2794	$183.28	$183.30	$183.30
Purchase #2	$56.94	4.479%	$59.4903	$59.49	$59.50	$59.50
Purchase #3	$114.65	3.584%	$118.7591	$118.76	$118.75	$118.80
Purchase #4	$149.95	9.566%	$164.2942	$164.29	$164.30	$164.30
Purchase #5	$66.94	7.536%	$71.9846	$71.98	$72.00	$72.00
Purchase #6	$60.48	10.547%	$66.8588	$66.86	$66.85	$66.90
Purchase #7	$74.31	5.802%	$78.6215	$78.62	$78.60	$78.60
7 purchase totals =	$696.96		$743.2879	$743.28	$743.30	$743.40