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	$157.78	9.574%	$172.8859	$172.89	$172.90	$172.90
Purchase #2	$248.96	9.190%	$271.8394	$271.84	$271.85	$271.80
Purchase #3	$186.73	3.797%	$193.8201	$193.82	$193.80	$193.80
Purchase #4	$86.88	4.567%	$90.8478	$90.85	$90.85	$90.80
Purchase #5	$107.60	13.420%	$122.0399	$122.04	$122.05	$122.00
Purchase #6	$13.87	12.315%	$15.5781	$15.58	$15.60	$15.60
Purchase #7	$102.27	8.772%	$111.2411	$111.24	$111.25	$111.20
7 purchase totals =	$904.09		$978.2523	$978.26	$978.30	$978.10