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	$6.28	5.575%	$6.6301	$6.63	$6.65	$6.60
Purchase #2	$60.30	4.791%	$63.189	$63.19	$63.20	$63.20
Purchase #3	$191.92	13.143%	$217.144	$217.14	$217.15	$217.10
Purchase #4	$223.59	6.483%	$238.0853	$238.09	$238.10	$238.10
Purchase #5	$206.59	13.489%	$234.4569	$234.46	$234.45	$234.50
Purchase #6	$37.54	5.484%	$39.5987	$39.60	$39.60	$39.60
Purchase #7	$238.72	6.845%	$255.0604	$255.06	$255.05	$255.10
7 purchase totals =	$964.94		$1,054.1644	$1,054.17	$1,054.20	$1,054.20