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	$79.64	11.323%	$88.6576	$88.66	$88.65	$88.70
Purchase #2	$119.90	5.595%	$126.6084	$126.61	$126.60	$126.60
Purchase #3	$76.43	12.261%	$85.8011	$85.80	$85.80	$85.80
Purchase #4	$162.67	11.605%	$181.5479	$181.55	$181.55	$181.50
Purchase #5	$99.60	4.163%	$103.7463	$103.75	$103.75	$103.70
Purchase #6	$233.83	3.520%	$242.0608	$242.06	$242.05	$242.10
Purchase #7	$74.83	13.600%	$85.0069	$85.01	$85.00	$85.00
7 purchase totals =	$846.90		$913.4290	$913.44	$913.40	$913.40