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	$38.63	7.399%	$41.4882	$41.49	$41.50	$41.50
Purchase #2	$97.29	10.826%	$107.8226	$107.82	$107.80	$107.80
Purchase #3	$49.64	13.849%	$56.5146	$56.51	$56.50	$56.50
Purchase #4	$32.55	3.160%	$33.5786	$33.58	$33.60	$33.60
Purchase #5	$65.31	9.785%	$71.7006	$71.70	$71.70	$71.70
Purchase #6	$141.66	8.847%	$154.1927	$154.19	$154.20	$154.20
Purchase #7	$52.66	13.698%	$59.8734	$59.87	$59.85	$59.90
7 purchase totals =	$477.74		$525.1707	$525.16	$525.15	$525.20