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	$74.75	5.530%	$78.8837	$78.88	$78.90	$78.90
Purchase #2	$34.64	12.111%	$38.8353	$38.84	$38.85	$38.80
Purchase #3	$107.38	3.634%	$111.2822	$111.28	$111.30	$111.30
Purchase #4	$243.63	11.845%	$272.488	$272.49	$272.50	$272.50
Purchase #5	$184.28	5.727%	$194.8337	$194.83	$194.85	$194.80
Purchase #6	$174.63	13.758%	$198.6556	$198.66	$198.65	$198.70
Purchase #7	$199.82	8.503%	$216.8107	$216.81	$216.80	$216.80
7 purchase totals =	$1,019.13		$1,111.7892	$1,111.79	$1,111.85	$1,111.80