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	$79.62	11.791%	$89.008	$89.01	$89.00	$89.00
Purchase #2	$104.87	3.772%	$108.8257	$108.83	$108.85	$108.80
Purchase #3	$38.82	13.651%	$44.1193	$44.12	$44.10	$44.10
Purchase #4	$17.43	11.221%	$19.3858	$19.39	$19.40	$19.40
Purchase #5	$231.40	10.785%	$256.3565	$256.36	$256.35	$256.40
Purchase #6	$38.34	13.277%	$43.4304	$43.43	$43.45	$43.40
Purchase #7	$56.99	7.387%	$61.1999	$61.20	$61.20	$61.20
7 purchase totals =	$567.47		$622.3256	$622.34	$622.35	$622.30