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	$9.81	6.238%	$10.4219	$10.42	$10.40	$10.40
Purchase #2	$158.72	10.502%	$175.3888	$175.39	$175.40	$175.40
Purchase #3	$131.81	3.360%	$136.2388	$136.24	$136.25	$136.20
Purchase #4	$208.61	8.274%	$225.8704	$225.87	$225.85	$225.90
Purchase #5	$38.87	7.488%	$41.7806	$41.78	$41.80	$41.80
Purchase #6	$142.39	5.460%	$150.1645	$150.16	$150.15	$150.20
Purchase #7	$118.89	8.353%	$128.8209	$128.82	$128.80	$128.80
7 purchase totals =	$809.10		$868.6859	$868.68	$868.65	$868.70