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	$159.77	8.856%	$173.9192	$173.92	$173.90	$173.90
Purchase #2	$76.92	10.512%	$85.0058	$85.01	$85.00	$85.00
Purchase #3	$43.70	6.412%	$46.502	$46.50	$46.50	$46.50
Purchase #4	$223.70	9.176%	$244.2267	$244.23	$244.25	$244.20
Purchase #5	$162.77	5.584%	$171.8591	$171.86	$171.85	$171.90
Purchase #6	$22.96	10.619%	$25.3981	$25.40	$25.40	$25.40
Purchase #7	$83.72	4.660%	$87.6214	$87.62	$87.60	$87.60
7 purchase totals =	$773.54		$834.5323	$834.54	$834.50	$834.50