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	$233.75	5.847%	$247.4174	$247.42	$247.40	$247.40
Purchase #2	$34.67	11.148%	$38.535	$38.54	$38.55	$38.50
Purchase #3	$107.80	6.515%	$114.8232	$114.82	$114.80	$114.80
Purchase #4	$87.34	3.534%	$90.4266	$90.43	$90.45	$90.40
Purchase #5	$11.55	10.247%	$12.7335	$12.73	$12.75	$12.70
Purchase #6	$61.76	7.367%	$66.3099	$66.31	$66.30	$66.30
Purchase #7	$9.72	3.449%	$10.0552	$10.06	$10.05	$10.10
7 purchase totals =	$546.59		$580.3008	$580.31	$580.30	$580.20