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	$158.84	8.867%	$172.9243	$172.92	$172.90	$172.90
Purchase #2	$7.57	10.646%	$8.3759	$8.38	$8.40	$8.40
Purchase #3	$94.92	9.623%	$104.0542	$104.05	$104.05	$104.10
Purchase #4	$56.52	10.767%	$62.6055	$62.61	$62.60	$62.60
Purchase #5	$21.92	11.194%	$24.3737	$24.37	$24.35	$24.40
Purchase #6	$15.40	12.834%	$17.3764	$17.38	$17.40	$17.40
Purchase #7	$45.40	13.461%	$51.5113	$51.51	$51.50	$51.50
7 purchase totals =	$400.57		$441.2213	$441.22	$441.20	$441.30