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	$54.78	9.627%	$60.0537	$60.05	$60.05	$60.10
Purchase #2	$224.45	11.659%	$250.6186	$250.62	$250.60	$250.60
Purchase #3	$92.40	13.836%	$105.1845	$105.18	$105.20	$105.20
Purchase #4	$186.87	6.377%	$198.7867	$198.79	$198.80	$198.80
Purchase #5	$94.60	4.647%	$98.9961	$99.00	$99.00	$99.00
Purchase #6	$63.40	10.833%	$70.2681	$70.27	$70.25	$70.30
Purchase #7	$98.82	4.636%	$103.4013	$103.40	$103.40	$103.40
7 purchase totals =	$815.32		$887.3090	$887.31	$887.30	$887.40