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	$165.59	10.593%	$183.1309	$183.13	$183.15	$183.10
Purchase #2	$176.36	12.361%	$198.1599	$198.16	$198.15	$198.20
Purchase #3	$39.53	3.670%	$40.9808	$40.98	$41.00	$41.00
Purchase #4	$176.50	5.748%	$186.6452	$186.65	$186.65	$186.60
Purchase #5	$65.89	9.757%	$72.3189	$72.32	$72.30	$72.30
Purchase #6	$126.50	10.356%	$139.6003	$139.60	$139.60	$139.60
Purchase #7	$155.47	13.575%	$176.5751	$176.58	$176.60	$176.60
7 purchase totals =	$905.84		$997.4111	$997.42	$997.45	$997.40