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	$85.65	5.434%	$90.3042	$90.30	$90.30	$90.30
Purchase #2	$24.50	6.757%	$26.1555	$26.16	$26.15	$26.20
Purchase #3	$65.29	11.754%	$72.9642	$72.96	$72.95	$73.00
Purchase #4	$12.83	4.675%	$13.4298	$13.43	$13.45	$13.40
Purchase #5	$123.25	8.749%	$134.0331	$134.03	$134.05	$134.00
Purchase #6	$158.59	10.856%	$175.8065	$175.81	$175.80	$175.80
Purchase #7	$72.81	10.604%	$80.5308	$80.53	$80.55	$80.50
7 purchase totals =	$542.92		$593.2241	$593.22	$593.25	$593.20