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	$85.31	5.592%	$90.0805	$90.08	$90.10	$90.10
Purchase #2	$155.45	4.661%	$162.6955	$162.70	$162.70	$162.70
Purchase #3	$132.86	6.639%	$141.6806	$141.68	$141.70	$141.70
Purchase #4	$106.49	7.262%	$114.2233	$114.22	$114.20	$114.20
Purchase #5	$142.50	11.182%	$158.4344	$158.43	$158.45	$158.40
Purchase #6	$52.32	7.590%	$56.2911	$56.29	$56.30	$56.30
Purchase #7	$151.95	7.218%	$162.9178	$162.92	$162.90	$162.90
7 purchase totals =	$826.88		$886.3232	$886.32	$886.35	$886.30