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	$144.66	8.162%	$156.4671	$156.47	$156.45	$156.50
Purchase #2	$51.86	7.362%	$55.6779	$55.68	$55.70	$55.70
Purchase #3	$119.77	5.348%	$126.1753	$126.18	$126.20	$126.20
Purchase #4	$116.76	10.444%	$128.9544	$128.95	$128.95	$129.00
Purchase #5	$135.38	11.746%	$151.2817	$151.28	$151.30	$151.30
Purchase #6	$159.89	6.251%	$169.8847	$169.88	$169.90	$169.90
Purchase #7	$76.51	3.143%	$78.9147	$78.91	$78.90	$78.90
7 purchase totals =	$804.83		$867.3558	$867.35	$867.40	$867.50