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	$221.34	8.698%	$240.5922	$240.59	$240.60	$240.60
Purchase #2	$11.68	8.659%	$12.6914	$12.69	$12.70	$12.70
Purchase #3	$96.60	7.156%	$103.5127	$103.51	$103.50	$103.50
Purchase #4	$93.42	7.403%	$100.3359	$100.34	$100.35	$100.30
Purchase #5	$115.60	10.130%	$127.3103	$127.31	$127.30	$127.30
Purchase #6	$217.40	11.134%	$241.6053	$241.61	$241.60	$241.60
Purchase #7	$244.84	13.185%	$277.1222	$277.12	$277.10	$277.10
7 purchase totals =	$1,000.88		$1,103.1700	$1,103.17	$1,103.15	$1,103.10