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	$219.35	6.382%	$233.3489	$233.35	$233.35	$233.30
Purchase #2	$41.50	3.196%	$42.8263	$42.83	$42.85	$42.80
Purchase #3	$104.54	13.697%	$118.8588	$118.86	$118.85	$118.90
Purchase #4	$45.37	3.733%	$47.0637	$47.06	$47.05	$47.10
Purchase #5	$50.99	7.462%	$54.7949	$54.79	$54.80	$54.80
Purchase #6	$181.56	4.874%	$190.4092	$190.41	$190.40	$190.40
Purchase #7	$134.29	6.724%	$143.3197	$143.32	$143.30	$143.30
7 purchase totals =	$777.60		$830.6215	$830.62	$830.60	$830.60