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	$153.85	9.361%	$168.2519	$168.25	$168.25	$168.30
Purchase #2	$193.52	11.313%	$215.4129	$215.41	$215.40	$215.40
Purchase #3	$18.85	8.731%	$20.4958	$20.50	$20.50	$20.50
Purchase #4	$86.74	3.398%	$89.6874	$89.69	$89.70	$89.70
Purchase #5	$74.44	11.205%	$82.781	$82.78	$82.80	$82.80
Purchase #6	$134.77	6.874%	$144.0341	$144.03	$144.05	$144.00
Purchase #7	$227.84	10.794%	$252.433	$252.43	$252.45	$252.40
7 purchase totals =	$890.01		$973.0961	$973.09	$973.15	$973.10