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	$30.25	11.862%	$33.8383	$33.84	$33.85	$33.80
Purchase #2	$107.83	4.405%	$112.5799	$112.58	$112.60	$112.60
Purchase #3	$53.38	13.242%	$60.4486	$60.45	$60.45	$60.40
Purchase #4	$102.34	9.387%	$111.9467	$111.95	$111.95	$111.90
Purchase #5	$16.93	9.508%	$18.5397	$18.54	$18.55	$18.50
Purchase #6	$5.33	6.112%	$5.6558	$5.66	$5.65	$5.70
Purchase #7	$10.90	4.690%	$11.4112	$11.41	$11.40	$11.40
7 purchase totals =	$326.96		$354.4202	$354.43	$354.45	$354.30