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	$22.25	10.278%	$24.5369	$24.54	$24.55	$24.50
Purchase #2	$127.94	13.791%	$145.5842	$145.58	$145.60	$145.60
Purchase #3	$17.88	5.804%	$18.9178	$18.92	$18.90	$18.90
Purchase #4	$119.97	11.214%	$133.4234	$133.42	$133.40	$133.40
Purchase #5	$93.78	5.522%	$98.9585	$98.96	$98.95	$99.00
Purchase #6	$54.37	10.107%	$59.8652	$59.87	$59.85	$59.90
Purchase #7	$96.31	11.424%	$107.3125	$107.31	$107.30	$107.30
7 purchase totals =	$532.50		$588.5985	$588.60	$588.55	$588.60