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	$11.83	12.364%	$13.2927	$13.29	$13.30	$13.30
Purchase #2	$238.37	7.469%	$256.1739	$256.17	$256.15	$256.20
Purchase #3	$112.90	9.763%	$123.9224	$123.92	$123.90	$123.90
Purchase #4	$29.87	10.831%	$33.1052	$33.11	$33.10	$33.10
Purchase #5	$105.51	3.182%	$108.8673	$108.87	$108.85	$108.90
Purchase #6	$132.47	11.768%	$148.0591	$148.06	$148.05	$148.10
Purchase #7	$81.69	11.138%	$90.7886	$90.79	$90.80	$90.80
7 purchase totals =	$712.64		$774.2092	$774.21	$774.15	$774.30