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	$158.53	5.724%	$167.6043	$167.60	$167.60	$167.60
Purchase #2	$103.89	5.488%	$109.5915	$109.59	$109.60	$109.60
Purchase #3	$22.66	13.620%	$25.7463	$25.75	$25.75	$25.70
Purchase #4	$71.68	11.575%	$79.977	$79.98	$80.00	$80.00
Purchase #5	$63.38	10.568%	$70.078	$70.08	$70.10	$70.10
Purchase #6	$107.27	5.746%	$113.4337	$113.43	$113.45	$113.40
Purchase #7	$70.31	3.507%	$72.7758	$72.78	$72.80	$72.80
7 purchase totals =	$597.72		$639.2066	$639.21	$639.30	$639.20