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	$233.77	6.126%	$248.0908	$248.09	$248.10	$248.10
Purchase #2	$159.43	10.466%	$176.1159	$176.12	$176.10	$176.10
Purchase #3	$65.92	10.494%	$72.8376	$72.84	$72.85	$72.80
Purchase #4	$100.48	3.117%	$103.612	$103.61	$103.60	$103.60
Purchase #5	$74.32	9.122%	$81.0995	$81.10	$81.10	$81.10
Purchase #6	$222.85	8.535%	$241.8702	$241.87	$241.85	$241.90
Purchase #7	$29.79	12.301%	$33.4545	$33.45	$33.45	$33.50
7 purchase totals =	$886.56		$957.0805	$957.08	$957.05	$957.10