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	$151.45	12.136%	$169.83	$169.83	$169.85	$169.80
Purchase #2	$120.49	5.762%	$127.4326	$127.43	$127.45	$127.40
Purchase #3	$136.32	12.269%	$153.0451	$153.05	$153.05	$153.00
Purchase #4	$56.46	10.554%	$62.4188	$62.42	$62.40	$62.40
Purchase #5	$122.69	4.455%	$128.1558	$128.16	$128.15	$128.20
Purchase #6	$198.86	9.395%	$217.5429	$217.54	$217.55	$217.50
Purchase #7	$52.51	6.171%	$55.7504	$55.75	$55.75	$55.80
7 purchase totals =	$838.78		$914.1756	$914.18	$914.20	$914.10