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	$96.47	13.821%	$109.8031	$109.80	$109.80	$109.80
Purchase #2	$65.32	8.728%	$71.0211	$71.02	$71.00	$71.00
Purchase #3	$116.46	10.127%	$128.2539	$128.25	$128.25	$128.30
Purchase #4	$178.26	5.724%	$188.4636	$188.46	$188.45	$188.50
Purchase #5	$248.62	12.228%	$279.0213	$279.02	$279.00	$279.00
Purchase #6	$81.78	6.142%	$86.8029	$86.80	$86.80	$86.80
Purchase #7	$185.85	9.832%	$204.1228	$204.12	$204.10	$204.10
7 purchase totals =	$972.76		$1,067.4887	$1,067.47	$1,067.40	$1,067.50