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	$12.40	11.565%	$13.8341	$13.83	$13.85	$13.80
Purchase #2	$38.96	8.408%	$42.2358	$42.24	$42.25	$42.20
Purchase #3	$34.79	9.737%	$38.1775	$38.18	$38.20	$38.20
Purchase #4	$77.33	12.612%	$87.0829	$87.08	$87.10	$87.10
Purchase #5	$94.98	5.578%	$100.278	$100.28	$100.30	$100.30
Purchase #6	$130.42	12.197%	$146.3273	$146.33	$146.35	$146.30
Purchase #7	$150.85	3.840%	$156.6426	$156.64	$156.65	$156.60
7 purchase totals =	$539.73		$584.5782	$584.58	$584.70	$584.50