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	$27.30	3.724%	$28.3167	$28.32	$28.30	$28.30
Purchase #2	$208.29	3.301%	$215.1657	$215.17	$215.15	$215.20
Purchase #3	$35.82	6.519%	$38.1551	$38.16	$38.15	$38.20
Purchase #4	$77.58	6.708%	$82.7841	$82.78	$82.80	$82.80
Purchase #5	$214.26	13.611%	$243.4229	$243.42	$243.40	$243.40
Purchase #6	$91.51	9.255%	$99.9793	$99.98	$100.00	$100.00
Purchase #7	$167.45	3.331%	$173.0278	$173.03	$173.05	$173.00
7 purchase totals =	$822.21		$880.8516	$880.86	$880.85	$880.90