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	$51.94	7.196%	$55.6776	$55.68	$55.70	$55.70
Purchase #2	$99.81	5.256%	$105.056	$105.06	$105.05	$105.10
Purchase #3	$118.71	4.389%	$123.9202	$123.92	$123.90	$123.90
Purchase #4	$102.88	13.792%	$117.0692	$117.07	$117.05	$117.10
Purchase #5	$187.53	13.277%	$212.4284	$212.43	$212.45	$212.40
Purchase #6	$65.45	9.784%	$71.8536	$71.85	$71.85	$71.90
Purchase #7	$40.83	12.716%	$46.0219	$46.02	$46.00	$46.00
7 purchase totals =	$667.15		$732.0269	$732.03	$732.00	$732.10