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	$163.58	9.277%	$178.7553	$178.76	$178.75	$178.80
Purchase #2	$153.89	11.301%	$171.2811	$171.28	$171.30	$171.30
Purchase #3	$131.88	8.874%	$143.583	$143.58	$143.60	$143.60
Purchase #4	$79.78	12.785%	$89.9799	$89.98	$90.00	$90.00
Purchase #5	$17.27	12.489%	$19.4269	$19.43	$19.45	$19.40
Purchase #6	$138.80	5.190%	$146.0037	$146.00	$146.00	$146.00
Purchase #7	$33.55	11.361%	$37.3616	$37.36	$37.35	$37.40
7 purchase totals =	$718.75		$786.3915	$786.39	$786.45	$786.50