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	$82.58	9.222%	$90.1955	$90.20	$90.20	$90.20
Purchase #2	$230.78	7.250%	$247.5116	$247.51	$247.50	$247.50
Purchase #3	$155.89	6.608%	$166.1912	$166.19	$166.20	$166.20
Purchase #4	$157.94	4.381%	$164.8594	$164.86	$164.85	$164.90
Purchase #5	$164.76	5.416%	$173.6834	$173.68	$173.70	$173.70
Purchase #6	$231.27	10.556%	$255.6829	$255.68	$255.70	$255.70
Purchase #7	$80.52	8.685%	$87.5132	$87.51	$87.50	$87.50
7 purchase totals =	$1,103.74		$1,185.6372	$1,185.63	$1,185.65	$1,185.70