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	$153.98	12.218%	$172.7933	$172.79	$172.80	$172.80
Purchase #2	$233.51	4.162%	$243.2287	$243.23	$243.25	$243.20
Purchase #3	$46.71	8.435%	$50.65	$50.65	$50.65	$50.70
Purchase #4	$70.42	11.634%	$78.6127	$78.61	$78.60	$78.60
Purchase #5	$55.78	13.710%	$63.4274	$63.43	$63.45	$63.40
Purchase #6	$57.60	8.419%	$62.4493	$62.45	$62.45	$62.40
Purchase #7	$142.62	6.201%	$151.4639	$151.46	$151.45	$151.50
7 purchase totals =	$760.62		$822.6253	$822.62	$822.65	$822.60