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	$221.46	13.355%	$251.036	$251.04	$251.05	$251.00
Purchase #2	$153.58	3.434%	$158.8539	$158.85	$158.85	$158.90
Purchase #3	$90.85	9.870%	$99.8169	$99.82	$99.80	$99.80
Purchase #4	$60.86	8.585%	$66.0848	$66.08	$66.10	$66.10
Purchase #5	$240.46	12.389%	$270.2506	$270.25	$270.25	$270.30
Purchase #6	$112.92	11.307%	$125.6879	$125.69	$125.70	$125.70
Purchase #7	$137.97	12.763%	$155.5791	$155.58	$155.60	$155.60
7 purchase totals =	$1,018.10		$1,127.3092	$1,127.31	$1,127.35	$1,127.40