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	$35.81	10.357%	$39.5188	$39.52	$39.50	$39.50
Purchase #2	$130.89	3.862%	$135.945	$135.95	$135.95	$135.90
Purchase #3	$96.28	13.113%	$108.9052	$108.91	$108.90	$108.90
Purchase #4	$60.43	8.142%	$65.3502	$65.35	$65.35	$65.40
Purchase #5	$150.75	11.583%	$168.2114	$168.21	$168.20	$168.20
Purchase #6	$143.49	5.819%	$151.8397	$151.84	$151.85	$151.80
Purchase #7	$95.65	5.528%	$100.9375	$100.94	$100.95	$100.90
7 purchase totals =	$713.30		$770.7078	$770.72	$770.70	$770.60