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	$160.78	13.751%	$182.8889	$182.89	$182.90	$182.90
Purchase #2	$190.32	5.450%	$200.6924	$200.69	$200.70	$200.70
Purchase #3	$86.91	4.152%	$90.5185	$90.52	$90.50	$90.50
Purchase #4	$200.95	12.679%	$226.4285	$226.43	$226.45	$226.40
Purchase #5	$213.33	13.866%	$242.9103	$242.91	$242.90	$242.90
Purchase #6	$50.35	13.239%	$57.0158	$57.02	$57.00	$57.00
Purchase #7	$218.50	5.289%	$230.0565	$230.06	$230.05	$230.10
7 purchase totals =	$1,121.14		$1,230.5109	$1,230.52	$1,230.50	$1,230.50