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	$97.79	3.109%	$100.8303	$100.83	$100.85	$100.80
Purchase #2	$199.65	11.597%	$222.8034	$222.80	$222.80	$222.80
Purchase #3	$53.59	12.530%	$60.3048	$60.30	$60.30	$60.30
Purchase #4	$158.93	11.301%	$176.8907	$176.89	$176.90	$176.90
Purchase #5	$178.30	3.178%	$183.9664	$183.97	$183.95	$184.00
Purchase #6	$39.65	4.661%	$41.4981	$41.50	$41.50	$41.50
Purchase #7	$69.87	6.289%	$74.2641	$74.26	$74.25	$74.30
7 purchase totals =	$797.78		$860.5578	$860.55	$860.55	$860.60