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	$6.55	8.268%	$7.0916	$7.09	$7.10	$7.10
Purchase #2	$240.37	12.301%	$269.9379	$269.94	$269.95	$269.90
Purchase #3	$79.50	8.556%	$86.302	$86.30	$86.30	$86.30
Purchase #4	$134.38	6.804%	$143.5232	$143.52	$143.50	$143.50
Purchase #5	$150.34	5.194%	$158.1487	$158.15	$158.15	$158.10
Purchase #6	$49.85	10.643%	$55.1555	$55.16	$55.15	$55.20
Purchase #7	$177.53	5.523%	$187.335	$187.34	$187.35	$187.30
7 purchase totals =	$838.52		$907.4939	$907.50	$907.50	$907.40