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	$46.94	7.253%	$50.3446	$50.34	$50.35	$50.30
Purchase #2	$92.62	3.633%	$95.9849	$95.98	$96.00	$96.00
Purchase #3	$179.43	6.397%	$190.9081	$190.91	$190.90	$190.90
Purchase #4	$20.93	4.262%	$21.822	$21.82	$21.80	$21.80
Purchase #5	$61.30	7.675%	$66.0048	$66.00	$66.00	$66.00
Purchase #6	$89.38	3.542%	$92.5458	$92.55	$92.55	$92.50
Purchase #7	$113.90	7.221%	$122.1247	$122.12	$122.10	$122.10
7 purchase totals =	$604.50		$639.7349	$639.72	$639.70	$639.60