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	$37.38	8.192%	$40.4422	$40.44	$40.45	$40.40
Purchase #2	$130.52	13.735%	$148.4469	$148.45	$148.45	$148.40
Purchase #3	$130.83	9.204%	$142.8716	$142.87	$142.85	$142.90
Purchase #4	$158.87	10.632%	$175.7611	$175.76	$175.75	$175.80
Purchase #5	$158.84	12.722%	$179.0476	$179.05	$179.05	$179.00
Purchase #6	$95.75	7.834%	$103.2511	$103.25	$103.25	$103.30
Purchase #7	$75.58	10.162%	$83.2604	$83.26	$83.25	$83.30
7 purchase totals =	$787.77		$873.0809	$873.08	$873.05	$873.10