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	$239.59	12.321%	$269.1099	$269.11	$269.10	$269.10
Purchase #2	$108.50	13.812%	$123.486	$123.49	$123.50	$123.50
Purchase #3	$48.30	4.813%	$50.6247	$50.62	$50.60	$50.60
Purchase #4	$63.72	12.830%	$71.8953	$71.90	$71.90	$71.90
Purchase #5	$97.64	5.316%	$102.8305	$102.83	$102.85	$102.80
Purchase #6	$45.46	6.462%	$48.3976	$48.40	$48.40	$48.40
Purchase #7	$100.29	11.597%	$111.9206	$111.92	$111.90	$111.90
7 purchase totals =	$703.50		$778.2646	$778.27	$778.25	$778.20