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	$17.45	8.549%	$18.9418	$18.94	$18.95	$18.90
Purchase #2	$43.50	9.297%	$47.5442	$47.54	$47.55	$47.50
Purchase #3	$65.78	11.649%	$73.4427	$73.44	$73.45	$73.40
Purchase #4	$19.41	3.601%	$20.109	$20.11	$20.10	$20.10
Purchase #5	$71.78	3.865%	$74.5543	$74.55	$74.55	$74.60
Purchase #6	$132.66	10.855%	$147.0602	$147.06	$147.05	$147.10
Purchase #7	$192.95	4.146%	$200.9497	$200.95	$200.95	$200.90
7 purchase totals =	$543.53		$582.6019	$582.59	$582.60	$582.50