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	$96.85	9.826%	$106.3665	$106.37	$106.35	$106.40
Purchase #2	$83.77	8.283%	$90.7087	$90.71	$90.70	$90.70
Purchase #3	$164.32	8.838%	$178.8426	$178.84	$178.85	$178.80
Purchase #4	$132.88	9.265%	$145.1913	$145.19	$145.20	$145.20
Purchase #5	$156.50	8.590%	$169.9434	$169.94	$169.95	$169.90
Purchase #6	$96.54	9.741%	$105.944	$105.94	$105.95	$105.90
Purchase #7	$226.72	6.814%	$242.1687	$242.17	$242.15	$242.20
7 purchase totals =	$957.58		$1,039.1652	$1,039.16	$1,039.15	$1,039.10