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	$28.91	11.186%	$32.1439	$32.14	$32.15	$32.10
Purchase #2	$134.31	12.582%	$151.2089	$151.21	$151.20	$151.20
Purchase #3	$176.49	9.509%	$193.2724	$193.27	$193.25	$193.30
Purchase #4	$196.71	7.797%	$212.0475	$212.05	$212.05	$212.00
Purchase #5	$101.91	9.403%	$111.4926	$111.49	$111.50	$111.50
Purchase #6	$188.80	5.629%	$199.4276	$199.43	$199.45	$199.40
Purchase #7	$176.91	8.435%	$191.8324	$191.83	$191.85	$191.80
7 purchase totals =	$1,004.04		$1,091.4253	$1,091.42	$1,091.45	$1,091.30