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	$40.41	8.524%	$43.8545	$43.85	$43.85	$43.90
Purchase #2	$89.39	3.348%	$92.3828	$92.38	$92.40	$92.40
Purchase #3	$228.97	12.813%	$258.3079	$258.31	$258.30	$258.30
Purchase #4	$9.37	11.616%	$10.4584	$10.46	$10.45	$10.50
Purchase #5	$177.95	11.671%	$198.7185	$198.72	$198.70	$198.70
Purchase #6	$102.97	13.249%	$116.6125	$116.61	$116.60	$116.60
Purchase #7	$185.51	8.103%	$200.5419	$200.54	$200.55	$200.50
7 purchase totals =	$834.57		$920.8765	$920.87	$920.85	$920.90