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	$61.69	13.184%	$69.8232	$69.82	$69.80	$69.80
Purchase #2	$171.94	6.783%	$183.6027	$183.60	$183.60	$183.60
Purchase #3	$33.57	12.122%	$37.6394	$37.64	$37.65	$37.60
Purchase #4	$48.41	13.113%	$54.758	$54.76	$54.75	$54.80
Purchase #5	$99.41	11.745%	$111.0857	$111.09	$111.10	$111.10
Purchase #6	$116.45	9.663%	$127.7026	$127.70	$127.70	$127.70
Purchase #7	$57.97	5.701%	$61.2749	$61.27	$61.25	$61.30
7 purchase totals =	$589.44		$645.8865	$645.88	$645.85	$645.90