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	$72.30	11.633%	$80.7107	$80.71	$80.70	$80.70
Purchase #2	$103.60	7.717%	$111.5948	$111.59	$111.60	$111.60
Purchase #3	$127.85	4.687%	$133.8423	$133.84	$133.85	$133.80
Purchase #4	$48.46	5.616%	$51.1815	$51.18	$51.20	$51.20
Purchase #5	$31.72	8.543%	$34.4298	$34.43	$34.45	$34.40
Purchase #6	$132.66	6.333%	$141.0614	$141.06	$141.05	$141.10
Purchase #7	$215.90	5.355%	$227.4614	$227.46	$227.45	$227.50
7 purchase totals =	$732.49		$780.2819	$780.27	$780.30	$780.30