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	$35.78	10.268%	$39.4539	$39.45	$39.45	$39.50
Purchase #2	$13.69	3.620%	$14.1856	$14.19	$14.20	$14.20
Purchase #3	$98.93	4.841%	$103.7192	$103.72	$103.70	$103.70
Purchase #4	$23.31	5.240%	$24.5314	$24.53	$24.55	$24.50
Purchase #5	$40.96	10.685%	$45.3366	$45.34	$45.35	$45.30
Purchase #6	$157.71	10.191%	$173.7822	$173.78	$173.80	$173.80
Purchase #7	$115.87	6.211%	$123.0667	$123.07	$123.05	$123.10
7 purchase totals =	$486.25		$524.0756	$524.08	$524.10	$524.10