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	$46.68	10.347%	$51.51	$51.51	$51.50	$51.50
Purchase #2	$53.81	4.396%	$56.1755	$56.18	$56.20	$56.20
Purchase #3	$66.65	8.553%	$72.3506	$72.35	$72.35	$72.40
Purchase #4	$249.59	6.753%	$266.4448	$266.44	$266.45	$266.40
Purchase #5	$118.81	11.572%	$132.5587	$132.56	$132.55	$132.60
Purchase #6	$30.85	13.772%	$35.0987	$35.10	$35.10	$35.10
Purchase #7	$39.35	7.742%	$42.3965	$42.40	$42.40	$42.40
7 purchase totals =	$605.74		$656.5348	$656.54	$656.55	$656.60