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	$136.80	12.751%	$154.2434	$154.24	$154.25	$154.20
Purchase #2	$200.89	7.135%	$215.2235	$215.22	$215.20	$215.20
Purchase #3	$98.79	13.248%	$111.8777	$111.88	$111.90	$111.90
Purchase #4	$28.56	11.517%	$31.8493	$31.85	$31.85	$31.80
Purchase #5	$66.95	4.750%	$70.1301	$70.13	$70.15	$70.10
Purchase #6	$213.38	8.321%	$231.1353	$231.14	$231.15	$231.10
Purchase #7	$12.45	10.246%	$13.7256	$13.73	$13.75	$13.70
7 purchase totals =	$757.82		$828.1849	$828.19	$828.25	$828.00