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	$83.61	9.206%	$91.3071	$91.31	$91.30	$91.30
Purchase #2	$90.35	10.520%	$99.8548	$99.85	$99.85	$99.90
Purchase #3	$73.94	12.852%	$83.4428	$83.44	$83.45	$83.40
Purchase #4	$122.60	13.218%	$138.8053	$138.81	$138.80	$138.80
Purchase #5	$197.78	13.839%	$225.1508	$225.15	$225.15	$225.20
Purchase #6	$200.25	5.562%	$211.3879	$211.39	$211.40	$211.40
Purchase #7	$116.50	9.208%	$127.2273	$127.23	$127.25	$127.20
7 purchase totals =	$885.03		$977.1760	$977.18	$977.20	$977.20