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	$68.92	13.798%	$78.4296	$78.43	$78.45	$78.40
Purchase #2	$224.54	10.745%	$248.6668	$248.67	$248.65	$248.70
Purchase #3	$247.71	13.793%	$281.8766	$281.88	$281.90	$281.90
Purchase #4	$178.52	4.783%	$187.0586	$187.06	$187.05	$187.10
Purchase #5	$231.68	13.513%	$262.9869	$262.99	$263.00	$263.00
Purchase #6	$66.77	11.389%	$74.3744	$74.37	$74.35	$74.40
Purchase #7	$247.37	3.284%	$255.4936	$255.49	$255.50	$255.50
7 purchase totals =	$1,265.51		$1,388.8865	$1,388.89	$1,388.90	$1,389.00