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	$26.66	6.797%	$28.4721	$28.47	$28.45	$28.50
Purchase #2	$153.90	7.721%	$165.7826	$165.78	$165.80	$165.80
Purchase #3	$40.64	5.364%	$42.8199	$42.82	$42.80	$42.80
Purchase #4	$101.87	12.724%	$114.8319	$114.83	$114.85	$114.80
Purchase #5	$142.74	4.325%	$148.9135	$148.91	$148.90	$148.90
Purchase #6	$112.77	12.691%	$127.0816	$127.08	$127.10	$127.10
Purchase #7	$238.31	10.469%	$263.2587	$263.26	$263.25	$263.30
7 purchase totals =	$816.89		$891.1603	$891.15	$891.15	$891.20