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	$34.50	8.749%	$37.5184	$37.52	$37.50	$37.50
Purchase #2	$156.72	4.185%	$163.2787	$163.28	$163.30	$163.30
Purchase #3	$39.89	9.409%	$43.6433	$43.64	$43.65	$43.60
Purchase #4	$102.85	13.346%	$116.5764	$116.58	$116.60	$116.60
Purchase #5	$30.85	6.403%	$32.8253	$32.83	$32.85	$32.80
Purchase #6	$185.52	6.283%	$197.1762	$197.18	$197.20	$197.20
Purchase #7	$83.33	8.863%	$90.7155	$90.72	$90.70	$90.70
7 purchase totals =	$633.66		$681.7338	$681.75	$681.80	$681.70