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	$45.42	6.563%	$48.4009	$48.40	$48.40	$48.40
Purchase #2	$39.60	10.103%	$43.6008	$43.60	$43.60	$43.60
Purchase #3	$215.76	7.124%	$231.1307	$231.13	$231.15	$231.10
Purchase #4	$50.31	9.259%	$54.9682	$54.97	$54.95	$55.00
Purchase #5	$129.91	10.555%	$143.622	$143.62	$143.60	$143.60
Purchase #6	$55.34	7.336%	$59.3997	$59.40	$59.40	$59.40
Purchase #7	$224.52	4.683%	$235.0343	$235.03	$235.05	$235.00
7 purchase totals =	$760.86		$816.1566	$816.15	$816.15	$816.10