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	$56.70	13.666%	$64.4486	$64.45	$64.45	$64.40
Purchase #2	$137.37	7.852%	$148.1563	$148.16	$148.15	$148.20
Purchase #3	$232.96	9.147%	$254.2689	$254.27	$254.25	$254.30
Purchase #4	$47.82	13.135%	$54.1012	$54.10	$54.10	$54.10
Purchase #5	$27.97	4.714%	$29.2885	$29.29	$29.30	$29.30
Purchase #6	$93.28	6.637%	$99.471	$99.47	$99.45	$99.50
Purchase #7	$36.35	11.650%	$40.5848	$40.58	$40.60	$40.60
7 purchase totals =	$632.45		$690.3193	$690.32	$690.30	$690.40