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	$138.46	5.160%	$145.6045	$145.60	$145.60	$145.60
Purchase #2	$172.89	5.654%	$182.6652	$182.67	$182.65	$182.70
Purchase #3	$107.69	3.452%	$111.4075	$111.41	$111.40	$111.40
Purchase #4	$157.58	10.104%	$173.5019	$173.50	$173.50	$173.50
Purchase #5	$188.33	8.761%	$204.8296	$204.83	$204.85	$204.80
Purchase #6	$244.88	8.751%	$266.3094	$266.31	$266.30	$266.30
Purchase #7	$184.85	10.688%	$204.6068	$204.61	$204.60	$204.60
7 purchase totals =	$1,194.68		$1,288.9249	$1,288.93	$1,288.90	$1,288.90