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	$230.47	10.802%	$255.3654	$255.37	$255.35	$255.40
Purchase #2	$183.88	6.677%	$196.1577	$196.16	$196.15	$196.20
Purchase #3	$235.76	7.422%	$253.2581	$253.26	$253.25	$253.30
Purchase #4	$225.93	12.859%	$254.9823	$254.98	$255.00	$255.00
Purchase #5	$35.70	9.266%	$39.008	$39.01	$39.00	$39.00
Purchase #6	$226.29	12.455%	$254.4744	$254.47	$254.45	$254.50
Purchase #7	$48.51	7.478%	$52.1376	$52.14	$52.15	$52.10
7 purchase totals =	$1,186.54		$1,305.3835	$1,305.39	$1,305.35	$1,305.50