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	$222.56	5.286%	$234.3245	$234.32	$234.30	$234.30
Purchase #2	$112.48	12.162%	$126.1598	$126.16	$126.15	$126.20
Purchase #3	$119.43	7.308%	$128.1579	$128.16	$128.15	$128.20
Purchase #4	$159.86	8.563%	$173.5488	$173.55	$173.55	$173.50
Purchase #5	$33.71	6.239%	$35.8132	$35.81	$35.80	$35.80
Purchase #6	$53.88	10.587%	$59.5843	$59.58	$59.60	$59.60
Purchase #7	$11.35	10.353%	$12.5251	$12.53	$12.55	$12.50
7 purchase totals =	$713.27		$770.1136	$770.11	$770.10	$770.10