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	$67.92	6.730%	$72.491	$72.49	$72.50	$72.50
Purchase #2	$121.82	10.681%	$134.8316	$134.83	$134.85	$134.80
Purchase #3	$110.26	6.370%	$117.2836	$117.28	$117.30	$117.30
Purchase #4	$74.68	12.328%	$83.8866	$83.89	$83.90	$83.90
Purchase #5	$176.60	13.631%	$200.6723	$200.67	$200.65	$200.70
Purchase #6	$103.53	4.343%	$108.0263	$108.03	$108.05	$108.00
Purchase #7	$173.71	5.128%	$182.6178	$182.62	$182.60	$182.60
7 purchase totals =	$828.52		$899.8092	$899.81	$899.85	$899.80