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	$103.93	12.251%	$116.6625	$116.66	$116.65	$116.70
Purchase #2	$108.28	4.753%	$113.4265	$113.43	$113.45	$113.40
Purchase #3	$22.51	5.818%	$23.8196	$23.82	$23.80	$23.80
Purchase #4	$200.58	7.673%	$215.9705	$215.97	$215.95	$216.00
Purchase #5	$72.27	4.339%	$75.4058	$75.41	$75.40	$75.40
Purchase #6	$100.42	11.123%	$111.5897	$111.59	$111.60	$111.60
Purchase #7	$104.59	11.434%	$116.5488	$116.55	$116.55	$116.50
7 purchase totals =	$712.58		$773.4234	$773.43	$773.40	$773.40