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	$133.39	11.783%	$149.1073	$149.11	$149.10	$149.10
Purchase #2	$121.39	10.607%	$134.2658	$134.27	$134.25	$134.30
Purchase #3	$131.55	4.593%	$137.5921	$137.59	$137.60	$137.60
Purchase #4	$40.84	3.286%	$42.182	$42.18	$42.20	$42.20
Purchase #5	$80.58	13.422%	$91.3954	$91.40	$91.40	$91.40
Purchase #6	$17.41	8.209%	$18.8392	$18.84	$18.85	$18.80
Purchase #7	$37.72	7.452%	$40.5309	$40.53	$40.55	$40.50
7 purchase totals =	$562.88		$613.9127	$613.92	$613.95	$613.90