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	$238.59	13.112%	$269.8739	$269.87	$269.85	$269.90
Purchase #2	$11.72	13.600%	$13.3139	$13.31	$13.30	$13.30
Purchase #3	$51.89	4.191%	$54.0647	$54.06	$54.05	$54.10
Purchase #4	$5.48	7.357%	$5.8832	$5.88	$5.90	$5.90
Purchase #5	$10.33	6.434%	$10.9946	$10.99	$11.00	$11.00
Purchase #6	$14.55	7.178%	$15.5944	$15.59	$15.60	$15.60
Purchase #7	$115.30	11.185%	$128.1963	$128.20	$128.20	$128.20
7 purchase totals =	$447.86		$497.9210	$497.90	$497.90	$498.00