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	$91.51	13.693%	$104.0405	$104.04	$104.05	$104.00
Purchase #2	$64.86	11.425%	$72.2703	$72.27	$72.25	$72.30
Purchase #3	$234.83	4.687%	$245.8365	$245.84	$245.85	$245.80
Purchase #4	$120.83	13.525%	$137.1723	$137.17	$137.15	$137.20
Purchase #5	$151.60	10.216%	$167.0875	$167.09	$167.10	$167.10
Purchase #6	$43.64	8.787%	$47.4746	$47.47	$47.45	$47.50
Purchase #7	$141.91	9.606%	$155.5419	$155.54	$155.55	$155.50
7 purchase totals =	$849.18		$929.4236	$929.42	$929.40	$929.40