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	$33.75	12.762%	$38.0572	$38.06	$38.05	$38.10
Purchase #2	$139.31	9.415%	$152.426	$152.43	$152.45	$152.40
Purchase #3	$76.82	3.637%	$79.6139	$79.61	$79.60	$79.60
Purchase #4	$200.25	11.678%	$223.6352	$223.64	$223.65	$223.60
Purchase #5	$224.90	10.268%	$247.9927	$247.99	$248.00	$248.00
Purchase #6	$156.36	6.304%	$166.2169	$166.22	$166.20	$166.20
Purchase #7	$103.30	8.131%	$111.6993	$111.70	$111.70	$111.70
7 purchase totals =	$934.69		$1,019.6412	$1,019.65	$1,019.65	$1,019.60