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	$200.38	3.575%	$207.5436	$207.54	$207.55	$207.50
Purchase #2	$52.82	9.508%	$57.8421	$57.84	$57.85	$57.80
Purchase #3	$55.92	12.561%	$62.9441	$62.94	$62.95	$62.90
Purchase #4	$165.83	4.178%	$172.7584	$172.76	$172.75	$172.80
Purchase #5	$117.92	8.781%	$128.2746	$128.27	$128.25	$128.30
Purchase #6	$89.92	5.861%	$95.1902	$95.19	$95.20	$95.20
Purchase #7	$128.44	10.608%	$142.0649	$142.06	$142.05	$142.10
7 purchase totals =	$811.23		$866.6179	$866.60	$866.60	$866.60