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	$12.31	4.326%	$12.8425	$12.84	$12.85	$12.80
Purchase #2	$130.86	9.693%	$143.5443	$143.54	$143.55	$143.50
Purchase #3	$146.51	7.396%	$157.3459	$157.35	$157.35	$157.30
Purchase #4	$18.41	6.396%	$19.5875	$19.59	$19.60	$19.60
Purchase #5	$138.28	9.588%	$151.5383	$151.54	$151.55	$151.50
Purchase #6	$34.39	10.266%	$37.9205	$37.92	$37.90	$37.90
Purchase #7	$43.91	12.623%	$49.4528	$49.45	$49.45	$49.50
7 purchase totals =	$524.67		$572.2318	$572.23	$572.25	$572.10