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	$120.70	10.115%	$132.9088	$132.91	$132.90	$132.90
Purchase #2	$112.80	4.795%	$118.2088	$118.21	$118.20	$118.20
Purchase #3	$220.52	4.873%	$231.2659	$231.27	$231.25	$231.30
Purchase #4	$55.84	11.779%	$62.4174	$62.42	$62.40	$62.40
Purchase #5	$230.78	9.118%	$251.8225	$251.82	$251.80	$251.80
Purchase #6	$215.32	6.235%	$228.7452	$228.75	$228.75	$228.70
Purchase #7	$54.78	8.839%	$59.622	$59.62	$59.60	$59.60
7 purchase totals =	$1,010.74		$1,084.9906	$1,085.00	$1,084.90	$1,084.90