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	$18.28	11.759%	$20.4295	$20.43	$20.45	$20.40
Purchase #2	$54.27	5.629%	$57.3249	$57.32	$57.30	$57.30
Purchase #3	$60.59	4.858%	$63.5335	$63.53	$63.55	$63.50
Purchase #4	$173.25	12.133%	$194.2704	$194.27	$194.25	$194.30
Purchase #5	$11.49	4.670%	$12.0266	$12.03	$12.05	$12.00
Purchase #6	$155.90	4.247%	$162.5211	$162.52	$162.50	$162.50
Purchase #7	$79.92	4.356%	$83.4013	$83.40	$83.40	$83.40
7 purchase totals =	$553.70		$593.5073	$593.50	$593.50	$593.40