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	$60.37	7.135%	$64.6774	$64.68	$64.70	$64.70
Purchase #2	$115.53	10.435%	$127.5856	$127.59	$127.60	$127.60
Purchase #3	$128.38	13.342%	$145.5085	$145.51	$145.50	$145.50
Purchase #4	$166.96	5.159%	$175.5735	$175.57	$175.55	$175.60
Purchase #5	$78.30	13.874%	$89.1633	$89.16	$89.15	$89.20
Purchase #6	$169.53	8.438%	$183.8349	$183.83	$183.85	$183.80
Purchase #7	$129.44	11.147%	$143.8687	$143.87	$143.85	$143.90
7 purchase totals =	$848.51		$930.2119	$930.21	$930.20	$930.30