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	$134.94	3.630%	$139.8383	$139.84	$139.85	$139.80
Purchase #2	$86.92	4.579%	$90.9001	$90.90	$90.90	$90.90
Purchase #3	$143.59	5.642%	$151.6913	$151.69	$151.70	$151.70
Purchase #4	$10.80	5.169%	$11.3583	$11.36	$11.35	$11.40
Purchase #5	$92.72	8.410%	$100.5178	$100.52	$100.50	$100.50
Purchase #6	$215.72	12.588%	$242.8748	$242.87	$242.85	$242.90
Purchase #7	$154.79	4.725%	$162.1038	$162.10	$162.10	$162.10
7 purchase totals =	$839.48		$899.2844	$899.28	$899.25	$899.30