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	$91.46	10.384%	$100.9572	$100.96	$100.95	$101.00
Purchase #2	$165.70	6.403%	$176.3098	$176.31	$176.30	$176.30
Purchase #3	$156.52	10.164%	$172.4287	$172.43	$172.45	$172.40
Purchase #4	$187.43	5.868%	$198.4284	$198.43	$198.45	$198.40
Purchase #5	$213.28	11.829%	$238.5089	$238.51	$238.50	$238.50
Purchase #6	$78.54	8.662%	$85.3431	$85.34	$85.35	$85.30
Purchase #7	$16.30	7.831%	$17.5765	$17.58	$17.60	$17.60
7 purchase totals =	$909.23		$989.5526	$989.56	$989.60	$989.50