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	$32.39	7.371%	$34.7775	$34.78	$34.80	$34.80
Purchase #2	$48.80	6.658%	$52.0491	$52.05	$52.05	$52.00
Purchase #3	$89.25	4.810%	$93.5429	$93.54	$93.55	$93.50
Purchase #4	$244.75	13.591%	$278.014	$278.01	$278.00	$278.00
Purchase #5	$103.69	7.695%	$111.6689	$111.67	$111.65	$111.70
Purchase #6	$217.42	9.845%	$238.825	$238.83	$238.85	$238.80
Purchase #7	$102.64	4.659%	$107.422	$107.42	$107.40	$107.40
7 purchase totals =	$838.94		$916.2994	$916.30	$916.30	$916.20