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	$138.46	8.311%	$149.9674	$149.97	$149.95	$150.00
Purchase #2	$76.58	4.237%	$79.8247	$79.82	$79.80	$79.80
Purchase #3	$51.57	7.840%	$55.6131	$55.61	$55.60	$55.60
Purchase #4	$84.58	6.643%	$90.1986	$90.20	$90.20	$90.20
Purchase #5	$80.54	6.116%	$85.4658	$85.47	$85.45	$85.50
Purchase #6	$69.87	3.397%	$72.2435	$72.24	$72.25	$72.20
Purchase #7	$137.93	10.135%	$151.9092	$151.91	$151.90	$151.90
7 purchase totals =	$639.53		$685.2223	$685.22	$685.15	$685.20