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	$50.64	12.193%	$56.8145	$56.81	$56.80	$56.80
Purchase #2	$39.42	7.589%	$42.4116	$42.41	$42.40	$42.40
Purchase #3	$53.48	4.473%	$55.8722	$55.87	$55.85	$55.90
Purchase #4	$141.45	3.564%	$146.4913	$146.49	$146.50	$146.50
Purchase #5	$144.53	10.602%	$159.8531	$159.85	$159.85	$159.90
Purchase #6	$142.51	11.195%	$158.464	$158.46	$158.45	$158.50
Purchase #7	$25.27	3.470%	$26.1469	$26.15	$26.15	$26.10
7 purchase totals =	$597.30		$646.0536	$646.04	$646.00	$646.10