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	$48.33	12.675%	$54.4558	$54.46	$54.45	$54.50
Purchase #2	$12.98	11.480%	$14.4701	$14.47	$14.45	$14.50
Purchase #3	$17.80	4.256%	$18.5576	$18.56	$18.55	$18.60
Purchase #4	$100.53	7.499%	$108.0687	$108.07	$108.05	$108.10
Purchase #5	$125.79	13.555%	$142.8408	$142.84	$142.85	$142.80
Purchase #6	$158.87	10.767%	$175.9755	$175.98	$176.00	$176.00
Purchase #7	$139.45	6.228%	$148.1349	$148.13	$148.15	$148.10
7 purchase totals =	$603.75		$662.5034	$662.51	$662.50	$662.60