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	$63.92	3.335%	$66.0517	$66.05	$66.05	$66.10
Purchase #2	$72.32	8.788%	$78.6755	$78.68	$78.70	$78.70
Purchase #3	$223.67	7.254%	$239.895	$239.90	$239.90	$239.90
Purchase #4	$101.54	12.806%	$114.5432	$114.54	$114.55	$114.50
Purchase #5	$236.52	8.323%	$256.2056	$256.21	$256.20	$256.20
Purchase #6	$94.72	7.482%	$101.807	$101.81	$101.80	$101.80
Purchase #7	$119.58	3.392%	$123.6362	$123.64	$123.65	$123.60
7 purchase totals =	$912.27		$980.8142	$980.83	$980.85	$980.80