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	$35.85	8.543%	$38.9127	$38.91	$38.90	$38.90
Purchase #2	$139.54	3.304%	$144.1504	$144.15	$144.15	$144.20
Purchase #3	$160.52	11.353%	$178.7438	$178.74	$178.75	$178.70
Purchase #4	$89.76	10.763%	$99.4209	$99.42	$99.40	$99.40
Purchase #5	$107.44	4.649%	$112.4349	$112.43	$112.45	$112.40
Purchase #6	$111.41	4.732%	$116.6819	$116.68	$116.70	$116.70
Purchase #7	$245.78	5.125%	$258.3762	$258.38	$258.40	$258.40
7 purchase totals =	$890.30		$948.7208	$948.71	$948.75	$948.70