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	$14.71	5.672%	$15.5444	$15.54	$15.55	$15.50
Purchase #2	$38.91	10.306%	$42.9201	$42.92	$42.90	$42.90
Purchase #3	$118.45	7.288%	$127.0826	$127.08	$127.10	$127.10
Purchase #4	$16.49	6.250%	$17.5206	$17.52	$17.50	$17.50
Purchase #5	$224.38	13.737%	$255.2031	$255.20	$255.20	$255.20
Purchase #6	$212.26	12.158%	$238.0666	$238.07	$238.05	$238.10
Purchase #7	$96.35	9.589%	$105.589	$105.59	$105.60	$105.60
7 purchase totals =	$721.55		$801.9264	$801.92	$801.90	$801.90