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	$14.83	7.780%	$15.9838	$15.98	$16.00	$16.00
Purchase #2	$90.83	10.283%	$100.17	$100.17	$100.15	$100.20
Purchase #3	$103.63	4.740%	$108.5421	$108.54	$108.55	$108.50
Purchase #4	$247.76	9.664%	$271.7035	$271.70	$271.70	$271.70
Purchase #5	$27.55	13.396%	$31.2406	$31.24	$31.25	$31.20
Purchase #6	$49.65	4.532%	$51.9001	$51.90	$51.90	$51.90
Purchase #7	$46.93	10.555%	$51.8835	$51.88	$51.90	$51.90
7 purchase totals =	$581.18		$631.4236	$631.41	$631.45	$631.40