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	$16.56	11.838%	$18.5204	$18.52	$18.50	$18.50
Purchase #2	$144.66	6.731%	$154.3971	$154.40	$154.40	$154.40
Purchase #3	$57.83	11.820%	$64.6655	$64.67	$64.65	$64.70
Purchase #4	$222.77	4.196%	$232.1174	$232.12	$232.10	$232.10
Purchase #5	$68.68	13.662%	$78.0631	$78.06	$78.05	$78.10
Purchase #6	$238.94	10.278%	$263.4983	$263.50	$263.50	$263.50
Purchase #7	$232.28	6.846%	$248.1819	$248.18	$248.20	$248.20
7 purchase totals =	$981.72		$1,059.4437	$1,059.45	$1,059.40	$1,059.50