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	$7.55	11.602%	$8.426	$8.43	$8.45	$8.40
Purchase #2	$177.78	10.416%	$196.2976	$196.30	$196.30	$196.30
Purchase #3	$116.52	9.705%	$127.8283	$127.83	$127.85	$127.80
Purchase #4	$43.54	10.664%	$48.1831	$48.18	$48.20	$48.20
Purchase #5	$19.66	5.668%	$20.7743	$20.77	$20.75	$20.80
Purchase #6	$90.55	4.227%	$94.3775	$94.38	$94.40	$94.40
Purchase #7	$152.71	3.397%	$157.8976	$157.90	$157.90	$157.90
7 purchase totals =	$608.31		$653.7844	$653.79	$653.85	$653.80