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	$90.44	12.823%	$102.0371	$102.04	$102.05	$102.00
Purchase #2	$233.66	9.451%	$255.7432	$255.74	$255.75	$255.70
Purchase #3	$225.86	4.286%	$235.5404	$235.54	$235.55	$235.50
Purchase #4	$47.60	10.678%	$52.6827	$52.68	$52.70	$52.70
Purchase #5	$250.62	11.393%	$279.1731	$279.17	$279.15	$279.20
Purchase #6	$116.66	9.354%	$127.5724	$127.57	$127.55	$127.60
Purchase #7	$45.70	4.605%	$47.8045	$47.80	$47.80	$47.80
7 purchase totals =	$1,010.54		$1,100.5534	$1,100.54	$1,100.55	$1,100.50