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	$73.44	12.553%	$82.6589	$82.66	$82.65	$82.70
Purchase #2	$64.81	7.782%	$69.8535	$69.85	$69.85	$69.90
Purchase #3	$41.60	11.840%	$46.5254	$46.53	$46.55	$46.50
Purchase #4	$146.82	12.437%	$165.08	$165.08	$165.10	$165.10
Purchase #5	$53.51	6.615%	$57.0497	$57.05	$57.05	$57.00
Purchase #6	$119.37	6.839%	$127.5337	$127.53	$127.55	$127.50
Purchase #7	$114.49	3.217%	$118.1731	$118.17	$118.15	$118.20
7 purchase totals =	$614.04		$666.8743	$666.87	$666.90	$666.90