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	$48.82	13.696%	$55.5064	$55.51	$55.50	$55.50
Purchase #2	$155.51	3.173%	$160.4443	$160.44	$160.45	$160.40
Purchase #3	$127.89	12.457%	$143.8213	$143.82	$143.80	$143.80
Purchase #4	$204.28	12.271%	$229.3472	$229.35	$229.35	$229.30
Purchase #5	$52.43	5.674%	$55.4049	$55.40	$55.40	$55.40
Purchase #6	$59.65	10.154%	$65.7069	$65.71	$65.70	$65.70
Purchase #7	$7.29	12.858%	$8.2273	$8.23	$8.25	$8.20
7 purchase totals =	$655.87		$718.4583	$718.46	$718.45	$718.30