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	$34.80	9.679%	$38.1683	$38.17	$38.15	$38.20
Purchase #2	$147.34	6.468%	$156.87	$156.87	$156.85	$156.90
Purchase #3	$15.78	5.310%	$16.6179	$16.62	$16.60	$16.60
Purchase #4	$64.83	8.687%	$70.4618	$70.46	$70.45	$70.50
Purchase #5	$90.33	11.572%	$100.783	$100.78	$100.80	$100.80
Purchase #6	$188.32	4.485%	$196.7662	$196.77	$196.75	$196.80
Purchase #7	$173.59	13.148%	$196.4136	$196.41	$196.40	$196.40
7 purchase totals =	$714.99		$776.0808	$776.08	$776.00	$776.20