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	$28.89	7.785%	$31.1391	$31.14	$31.15	$31.10
Purchase #2	$84.65	5.163%	$89.0205	$89.02	$89.00	$89.00
Purchase #3	$130.29	13.672%	$148.1032	$148.10	$148.10	$148.10
Purchase #4	$38.27	5.398%	$40.3358	$40.34	$40.35	$40.30
Purchase #5	$14.60	8.203%	$15.7976	$15.80	$15.80	$15.80
Purchase #6	$224.32	11.702%	$250.5699	$250.57	$250.55	$250.60
Purchase #7	$49.41	13.576%	$56.1179	$56.12	$56.10	$56.10
7 purchase totals =	$570.43		$631.0840	$631.09	$631.05	$631.00