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	$82.93	6.615%	$88.4158	$88.42	$88.40	$88.40
Purchase #2	$235.63	9.810%	$258.7453	$258.75	$258.75	$258.70
Purchase #3	$104.90	6.504%	$111.7227	$111.72	$111.70	$111.70
Purchase #4	$229.45	5.696%	$242.5195	$242.52	$242.50	$242.50
Purchase #5	$95.46	8.331%	$103.4128	$103.41	$103.40	$103.40
Purchase #6	$30.41	12.338%	$34.162	$34.16	$34.15	$34.20
Purchase #7	$47.59	13.621%	$54.0722	$54.07	$54.05	$54.10
7 purchase totals =	$826.37		$893.0503	$893.05	$892.95	$893.00