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	$30.71	8.834%	$33.4229	$33.42	$33.40	$33.40
Purchase #2	$164.45	12.792%	$185.4864	$185.49	$185.50	$185.50
Purchase #3	$202.52	7.122%	$216.9435	$216.94	$216.95	$216.90
Purchase #4	$159.59	12.389%	$179.3616	$179.36	$179.35	$179.40
Purchase #5	$239.40	6.333%	$254.5612	$254.56	$254.55	$254.60
Purchase #6	$142.29	3.174%	$146.8063	$146.81	$146.80	$146.80
Purchase #7	$51.56	13.487%	$58.5139	$58.51	$58.50	$58.50
7 purchase totals =	$990.52		$1,075.0958	$1,075.09	$1,075.05	$1,075.10