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	$158.72	6.522%	$169.0717	$169.07	$169.05	$169.10
Purchase #2	$120.61	4.283%	$125.7757	$125.78	$125.80	$125.80
Purchase #3	$133.65	13.596%	$151.8211	$151.82	$151.80	$151.80
Purchase #4	$108.78	4.537%	$113.7153	$113.72	$113.70	$113.70
Purchase #5	$94.86	9.387%	$103.7645	$103.76	$103.75	$103.80
Purchase #6	$65.46	11.385%	$72.9126	$72.91	$72.90	$72.90
Purchase #7	$155.46	6.729%	$165.9209	$165.92	$165.90	$165.90
7 purchase totals =	$837.54		$902.9818	$902.98	$902.90	$903.00