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	$42.51	3.212%	$43.8754	$43.88	$43.90	$43.90
Purchase #2	$101.77	3.210%	$105.0368	$105.04	$105.05	$105.00
Purchase #3	$204.90	13.488%	$232.5369	$232.54	$232.55	$232.50
Purchase #4	$137.37	7.847%	$148.1494	$148.15	$148.15	$148.10
Purchase #5	$116.60	8.674%	$126.7139	$126.71	$126.70	$126.70
Purchase #6	$91.96	9.728%	$100.9059	$100.91	$100.90	$100.90
Purchase #7	$153.80	11.869%	$172.0545	$172.05	$172.05	$172.10
7 purchase totals =	$848.91		$929.2728	$929.28	$929.30	$929.20