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	$78.89	12.301%	$88.5943	$88.59	$88.60	$88.60
Purchase #2	$122.75	9.137%	$133.9657	$133.97	$133.95	$134.00
Purchase #3	$16.58	6.104%	$17.592	$17.59	$17.60	$17.60
Purchase #4	$35.83	13.289%	$40.5914	$40.59	$40.60	$40.60
Purchase #5	$39.58	9.274%	$43.2506	$43.25	$43.25	$43.30
Purchase #6	$249.50	5.724%	$263.7814	$263.78	$263.80	$263.80
Purchase #7	$97.69	3.231%	$100.8464	$100.85	$100.85	$100.80
7 purchase totals =	$640.82		$688.6218	$688.62	$688.65	$688.70