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	$151.26	11.467%	$168.605	$168.61	$168.60	$168.60
Purchase #2	$137.78	13.123%	$155.8609	$155.86	$155.85	$155.90
Purchase #3	$46.41	4.833%	$48.653	$48.65	$48.65	$48.70
Purchase #4	$32.32	7.798%	$34.8403	$34.84	$34.85	$34.80
Purchase #5	$100.43	8.691%	$109.1584	$109.16	$109.15	$109.20
Purchase #6	$151.44	13.258%	$171.5179	$171.52	$171.50	$171.50
Purchase #7	$137.90	10.201%	$151.9672	$151.97	$151.95	$152.00
7 purchase totals =	$757.54		$840.6027	$840.61	$840.55	$840.70