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	$134.36	10.248%	$148.1292	$148.13	$148.15	$148.10
Purchase #2	$37.77	9.217%	$41.2513	$41.25	$41.25	$41.30
Purchase #3	$153.64	13.199%	$173.9189	$173.92	$173.90	$173.90
Purchase #4	$29.78	6.190%	$31.6234	$31.62	$31.60	$31.60
Purchase #5	$102.51	11.710%	$114.5139	$114.51	$114.50	$114.50
Purchase #6	$127.75	4.395%	$133.3646	$133.36	$133.35	$133.40
Purchase #7	$48.96	12.565%	$55.1118	$55.11	$55.10	$55.10
7 purchase totals =	$634.77		$697.9131	$697.90	$697.85	$697.90