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	$143.25	6.219%	$152.1587	$152.16	$152.15	$152.20
Purchase #2	$123.94	12.383%	$139.2875	$139.29	$139.30	$139.30
Purchase #3	$249.88	11.688%	$279.086	$279.09	$279.10	$279.10
Purchase #4	$134.42	13.694%	$152.8275	$152.83	$152.85	$152.80
Purchase #5	$51.60	6.183%	$54.7904	$54.79	$54.80	$54.80
Purchase #6	$196.95	10.564%	$217.7558	$217.76	$217.75	$217.80
Purchase #7	$139.94	3.754%	$145.1933	$145.19	$145.20	$145.20
7 purchase totals =	$1,039.98		$1,141.0992	$1,141.11	$1,141.15	$1,141.20