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	$128.94	7.335%	$138.3977	$138.40	$138.40	$138.40
Purchase #2	$208.51	9.131%	$227.549	$227.55	$227.55	$227.50
Purchase #3	$210.50	11.535%	$234.7812	$234.78	$234.80	$234.80
Purchase #4	$43.78	13.554%	$49.7139	$49.71	$49.70	$49.70
Purchase #5	$114.76	11.215%	$127.6303	$127.63	$127.65	$127.60
Purchase #6	$156.28	5.566%	$164.9785	$164.98	$165.00	$165.00
Purchase #7	$129.39	13.192%	$146.4591	$146.46	$146.45	$146.50
7 purchase totals =	$992.16		$1,089.5097	$1,089.51	$1,089.55	$1,089.50