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	$139.64	13.836%	$158.9606	$158.96	$158.95	$159.00
Purchase #2	$34.66	3.336%	$35.8163	$35.82	$35.80	$35.80
Purchase #3	$177.25	13.310%	$200.842	$200.84	$200.85	$200.80
Purchase #4	$151.72	4.135%	$157.9936	$157.99	$158.00	$158.00
Purchase #5	$136.30	13.816%	$155.1312	$155.13	$155.15	$155.10
Purchase #6	$70.54	11.650%	$78.7579	$78.76	$78.75	$78.80
Purchase #7	$217.90	10.856%	$241.5552	$241.56	$241.55	$241.60
7 purchase totals =	$928.01		$1,029.0568	$1,029.06	$1,029.05	$1,029.10