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	$115.52	10.782%	$127.9754	$127.98	$128.00	$128.00
Purchase #2	$46.48	6.670%	$49.5802	$49.58	$49.60	$49.60
Purchase #3	$19.91	6.545%	$21.2131	$21.21	$21.20	$21.20
Purchase #4	$140.42	13.807%	$159.8078	$159.81	$159.80	$159.80
Purchase #5	$40.91	4.836%	$42.8884	$42.89	$42.90	$42.90
Purchase #6	$205.53	10.641%	$227.4004	$227.40	$227.40	$227.40
Purchase #7	$190.70	3.261%	$196.9187	$196.92	$196.90	$196.90
7 purchase totals =	$759.47		$825.7840	$825.79	$825.80	$825.80