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	$32.44	13.745%	$36.8989	$36.90	$36.90	$36.90
Purchase #2	$22.51	10.714%	$24.9217	$24.92	$24.90	$24.90
Purchase #3	$11.55	7.816%	$12.4527	$12.45	$12.45	$12.50
Purchase #4	$17.72	5.606%	$18.7134	$18.71	$18.70	$18.70
Purchase #5	$13.26	8.196%	$14.3468	$14.35	$14.35	$14.30
Purchase #6	$157.83	9.524%	$172.8617	$172.86	$172.85	$172.90
Purchase #7	$43.52	3.863%	$45.2012	$45.20	$45.20	$45.20
7 purchase totals =	$298.83		$325.3964	$325.39	$325.35	$325.40