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	$111.85	4.519%	$116.9045	$116.90	$116.90	$116.90
Purchase #2	$106.33	11.784%	$118.8599	$118.86	$118.85	$118.90
Purchase #3	$18.67	10.252%	$20.584	$20.58	$20.60	$20.60
Purchase #4	$21.47	4.427%	$22.4205	$22.42	$22.40	$22.40
Purchase #5	$226.42	12.849%	$255.5127	$255.51	$255.50	$255.50
Purchase #6	$107.70	5.778%	$113.9229	$113.92	$113.90	$113.90
Purchase #7	$125.39	5.315%	$132.0545	$132.05	$132.05	$132.10
7 purchase totals =	$717.83		$780.2590	$780.24	$780.20	$780.30