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	$150.50	5.106%	$158.1845	$158.18	$158.20	$158.20
Purchase #2	$34.71	10.719%	$38.4306	$38.43	$38.45	$38.40
Purchase #3	$120.69	3.243%	$124.604	$124.60	$124.60	$124.60
Purchase #4	$161.47	13.243%	$182.8535	$182.85	$182.85	$182.90
Purchase #5	$151.39	12.535%	$170.3667	$170.37	$170.35	$170.40
Purchase #6	$98.34	7.136%	$105.3575	$105.36	$105.35	$105.40
Purchase #7	$18.78	8.109%	$20.3029	$20.30	$20.30	$20.30
7 purchase totals =	$735.88		$800.0997	$800.09	$800.10	$800.20