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	$137.33	9.733%	$150.6963	$150.70	$150.70	$150.70
Purchase #2	$186.88	7.483%	$200.8642	$200.86	$200.85	$200.90
Purchase #3	$151.75	11.371%	$169.0055	$169.01	$169.00	$169.00
Purchase #4	$33.95	5.186%	$35.7106	$35.71	$35.70	$35.70
Purchase #5	$122.71	7.823%	$132.3096	$132.31	$132.30	$132.30
Purchase #6	$57.85	6.456%	$61.5848	$61.58	$61.60	$61.60
Purchase #7	$49.25	10.279%	$54.3124	$54.31	$54.30	$54.30
7 purchase totals =	$739.72		$804.4834	$804.48	$804.45	$804.50