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	$157.80	13.624%	$179.2987	$179.30	$179.30	$179.30
Purchase #2	$133.30	9.763%	$146.3141	$146.31	$146.30	$146.30
Purchase #3	$74.87	11.687%	$83.6201	$83.62	$83.60	$83.60
Purchase #4	$216.43	5.554%	$228.4505	$228.45	$228.45	$228.50
Purchase #5	$107.98	3.464%	$111.7204	$111.72	$111.70	$111.70
Purchase #6	$211.76	13.658%	$240.6822	$240.68	$240.70	$240.70
Purchase #7	$153.90	8.434%	$166.8799	$166.88	$166.90	$166.90
7 purchase totals =	$1,056.04		$1,156.9659	$1,156.96	$1,156.95	$1,157.00