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	$242.85	5.265%	$255.6361	$255.64	$255.65	$255.60
Purchase #2	$41.76	7.288%	$44.8035	$44.80	$44.80	$44.80
Purchase #3	$48.45	11.204%	$53.8783	$53.88	$53.90	$53.90
Purchase #4	$192.84	8.724%	$209.6634	$209.66	$209.65	$209.70
Purchase #5	$42.91	9.139%	$46.8315	$46.83	$46.85	$46.80
Purchase #6	$48.42	11.586%	$54.0299	$54.03	$54.05	$54.00
Purchase #7	$142.53	4.161%	$148.4607	$148.46	$148.45	$148.50
7 purchase totals =	$759.76		$813.3034	$813.30	$813.35	$813.30