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	$159.95	9.389%	$174.9677	$174.97	$174.95	$175.00
Purchase #2	$239.31	9.841%	$262.8605	$262.86	$262.85	$262.90
Purchase #3	$59.99	10.810%	$66.4749	$66.47	$66.45	$66.50
Purchase #4	$125.72	4.468%	$131.3372	$131.34	$131.35	$131.30
Purchase #5	$143.88	9.855%	$158.0594	$158.06	$158.05	$158.10
Purchase #6	$45.36	10.114%	$49.9477	$49.95	$49.95	$49.90
Purchase #7	$82.73	3.325%	$85.4808	$85.48	$85.50	$85.50
7 purchase totals =	$856.94		$929.1282	$929.13	$929.10	$929.20