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	$242.76	6.613%	$258.8137	$258.81	$258.80	$258.80
Purchase #2	$208.30	9.292%	$227.6552	$227.66	$227.65	$227.70
Purchase #3	$155.48	8.571%	$168.8062	$168.81	$168.80	$168.80
Purchase #4	$238.42	6.233%	$253.2807	$253.28	$253.30	$253.30
Purchase #5	$131.45	6.422%	$139.8917	$139.89	$139.90	$139.90
Purchase #6	$8.91	7.546%	$9.5823	$9.58	$9.60	$9.60
Purchase #7	$39.63	7.641%	$42.6581	$42.66	$42.65	$42.70
7 purchase totals =	$1,024.95		$1,100.6879	$1,100.69	$1,100.70	$1,100.80