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	$14.96	9.329%	$16.3556	$16.36	$16.35	$16.40
Purchase #2	$44.88	4.611%	$46.9494	$46.95	$46.95	$46.90
Purchase #3	$80.86	11.234%	$89.9438	$89.94	$89.95	$89.90
Purchase #4	$120.33	9.639%	$131.9286	$131.93	$131.95	$131.90
Purchase #5	$65.75	8.571%	$71.3854	$71.39	$71.40	$71.40
Purchase #6	$82.97	11.558%	$92.5597	$92.56	$92.55	$92.60
Purchase #7	$123.43	8.116%	$133.4476	$133.45	$133.45	$133.40
7 purchase totals =	$533.18		$582.5701	$582.58	$582.60	$582.50