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	$30.54	9.531%	$33.4508	$33.45	$33.45	$33.50
Purchase #2	$187.32	7.187%	$200.7827	$200.78	$200.80	$200.80
Purchase #3	$225.47	11.774%	$252.0168	$252.02	$252.00	$252.00
Purchase #4	$151.38	4.693%	$158.4843	$158.48	$158.50	$158.50
Purchase #5	$141.92	4.569%	$148.4043	$148.40	$148.40	$148.40
Purchase #6	$5.65	11.195%	$6.2825	$6.28	$6.30	$6.30
Purchase #7	$189.27	5.744%	$200.1417	$200.14	$200.15	$200.10
7 purchase totals =	$931.55		$999.5631	$999.55	$999.60	$999.60