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	$76.66	4.715%	$80.2745	$80.27	$80.25	$80.30
Purchase #2	$82.64	7.250%	$88.6314	$88.63	$88.65	$88.60
Purchase #3	$131.36	13.370%	$148.9228	$148.92	$148.90	$148.90
Purchase #4	$127.79	3.800%	$132.646	$132.65	$132.65	$132.60
Purchase #5	$107.72	3.359%	$111.3383	$111.34	$111.35	$111.30
Purchase #6	$62.52	5.156%	$65.7435	$65.74	$65.75	$65.70
Purchase #7	$74.33	9.593%	$81.4605	$81.46	$81.45	$81.50
7 purchase totals =	$663.02		$709.0170	$709.01	$709.00	$708.90