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	$221.45	10.810%	$245.3887	$245.39	$245.40	$245.40
Purchase #2	$79.77	4.531%	$83.3844	$83.38	$83.40	$83.40
Purchase #3	$156.58	10.475%	$172.9818	$172.98	$173.00	$173.00
Purchase #4	$168.78	12.683%	$190.1864	$190.19	$190.20	$190.20
Purchase #5	$43.91	3.575%	$45.4798	$45.48	$45.50	$45.50
Purchase #6	$66.85	7.708%	$72.0028	$72.00	$72.00	$72.00
Purchase #7	$104.33	6.792%	$111.4161	$111.42	$111.40	$111.40
7 purchase totals =	$841.67		$920.8400	$920.84	$920.90	$920.90