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	$146.64	13.462%	$166.3807	$166.38	$166.40	$166.40
Purchase #2	$204.91	6.674%	$218.5857	$218.59	$218.60	$218.60
Purchase #3	$139.70	8.252%	$151.228	$151.23	$151.25	$151.20
Purchase #4	$65.60	9.818%	$72.0406	$72.04	$72.05	$72.00
Purchase #5	$167.64	13.486%	$190.2479	$190.25	$190.25	$190.20
Purchase #6	$43.77	4.357%	$45.6771	$45.68	$45.70	$45.70
Purchase #7	$9.83	4.716%	$10.2936	$10.29	$10.30	$10.30
7 purchase totals =	$778.09		$854.4536	$854.46	$854.55	$854.40