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	$236.76	8.242%	$256.2738	$256.27	$256.25	$256.30
Purchase #2	$82.88	13.466%	$94.0406	$94.04	$94.05	$94.00
Purchase #3	$139.42	3.684%	$144.5562	$144.56	$144.55	$144.60
Purchase #4	$20.93	10.721%	$23.1739	$23.17	$23.15	$23.20
Purchase #5	$173.45	9.785%	$190.4221	$190.42	$190.40	$190.40
Purchase #6	$167.39	12.325%	$188.0208	$188.02	$188.00	$188.00
Purchase #7	$148.47	10.624%	$164.2435	$164.24	$164.25	$164.20
7 purchase totals =	$969.30		$1,060.7309	$1,060.72	$1,060.65	$1,060.70