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	$26.29	13.592%	$29.8633	$29.86	$29.85	$29.90
Purchase #2	$126.89	4.461%	$132.5506	$132.55	$132.55	$132.60
Purchase #3	$239.37	13.785%	$272.3672	$272.37	$272.35	$272.40
Purchase #4	$16.89	12.139%	$18.9403	$18.94	$18.95	$18.90
Purchase #5	$113.84	11.793%	$127.2652	$127.27	$127.25	$127.30
Purchase #6	$46.91	3.408%	$48.5087	$48.51	$48.50	$48.50
Purchase #7	$102.85	4.841%	$107.829	$107.83	$107.85	$107.80
7 purchase totals =	$673.04		$737.3243	$737.33	$737.30	$737.40