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	$201.46	11.291%	$224.2068	$224.21	$224.20	$224.20
Purchase #2	$28.64	4.255%	$29.8586	$29.86	$29.85	$29.90
Purchase #3	$118.46	7.640%	$127.5103	$127.51	$127.50	$127.50
Purchase #4	$113.37	6.294%	$120.5055	$120.51	$120.50	$120.50
Purchase #5	$74.84	5.389%	$78.8731	$78.87	$78.85	$78.90
Purchase #6	$56.85	12.553%	$63.9864	$63.99	$64.00	$64.00
Purchase #7	$231.89	13.664%	$263.5754	$263.58	$263.60	$263.60
7 purchase totals =	$825.51		$908.5161	$908.53	$908.50	$908.60