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	$101.87	9.838%	$111.892	$111.89	$111.90	$111.90
Purchase #2	$51.79	4.123%	$53.9253	$53.93	$53.95	$53.90
Purchase #3	$81.27	8.792%	$88.4153	$88.42	$88.40	$88.40
Purchase #4	$43.98	13.569%	$49.9476	$49.95	$49.95	$49.90
Purchase #5	$105.29	11.586%	$117.4889	$117.49	$117.50	$117.50
Purchase #6	$131.61	12.502%	$148.0639	$148.06	$148.05	$148.10
Purchase #7	$228.38	13.580%	$259.394	$259.39	$259.40	$259.40
7 purchase totals =	$744.19		$829.1270	$829.13	$829.15	$829.10