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	$8.97	12.109%	$10.0562	$10.06	$10.05	$10.10
Purchase #2	$150.90	13.250%	$170.8943	$170.89	$170.90	$170.90
Purchase #3	$5.94	12.512%	$6.6832	$6.68	$6.70	$6.70
Purchase #4	$190.75	11.422%	$212.5375	$212.54	$212.55	$212.50
Purchase #5	$25.95	13.104%	$29.3505	$29.35	$29.35	$29.40
Purchase #6	$128.83	4.185%	$134.2215	$134.22	$134.20	$134.20
Purchase #7	$78.44	5.188%	$82.5095	$82.51	$82.50	$82.50
7 purchase totals =	$589.78		$646.2527	$646.25	$646.25	$646.30