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	$28.28	4.661%	$29.5981	$29.60	$29.60	$29.60
Purchase #2	$10.72	12.665%	$12.0777	$12.08	$12.10	$12.10
Purchase #3	$190.91	12.565%	$214.8978	$214.90	$214.90	$214.90
Purchase #4	$115.87	10.295%	$127.7988	$127.80	$127.80	$127.80
Purchase #5	$6.52	4.582%	$6.8187	$6.82	$6.80	$6.80
Purchase #6	$197.67	9.340%	$216.1324	$216.13	$216.15	$216.10
Purchase #7	$52.95	13.652%	$60.1787	$60.18	$60.20	$60.20
7 purchase totals =	$602.92		$667.5022	$667.51	$667.55	$667.50