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	$65.37	9.829%	$71.7952	$71.80	$71.80	$71.80
Purchase #2	$203.31	9.291%	$222.1995	$222.20	$222.20	$222.20
Purchase #3	$180.38	4.133%	$187.8351	$187.84	$187.85	$187.80
Purchase #4	$74.55	3.683%	$77.2957	$77.30	$77.30	$77.30
Purchase #5	$124.50	11.717%	$139.0877	$139.09	$139.10	$139.10
Purchase #6	$157.79	5.612%	$166.6452	$166.65	$166.65	$166.60
Purchase #7	$94.50	10.575%	$104.4934	$104.49	$104.50	$104.50
7 purchase totals =	$900.40		$969.3518	$969.37	$969.40	$969.30