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	$32.39	6.365%	$34.4516	$34.45	$34.45	$34.50
Purchase #2	$13.68	4.799%	$14.3365	$14.34	$14.35	$14.30
Purchase #3	$244.28	4.600%	$255.5169	$255.52	$255.50	$255.50
Purchase #4	$16.94	11.457%	$18.8808	$18.88	$18.90	$18.90
Purchase #5	$109.57	4.364%	$114.3516	$114.35	$114.35	$114.40
Purchase #6	$71.43	3.602%	$74.0029	$74.00	$74.00	$74.00
Purchase #7	$109.88	5.155%	$115.5443	$115.54	$115.55	$115.50
7 purchase totals =	$598.17		$627.0846	$627.08	$627.10	$627.10