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	$237.57	6.565%	$253.1665	$253.17	$253.15	$253.20
Purchase #2	$83.46	7.154%	$89.4307	$89.43	$89.45	$89.40
Purchase #3	$104.65	12.752%	$117.995	$118.00	$118.00	$118.00
Purchase #4	$19.61	10.127%	$21.5959	$21.60	$21.60	$21.60
Purchase #5	$87.50	10.286%	$96.5003	$96.50	$96.50	$96.50
Purchase #6	$119.72	4.637%	$125.2714	$125.27	$125.25	$125.30
Purchase #7	$105.61	12.316%	$118.6169	$118.62	$118.60	$118.60
7 purchase totals =	$758.12		$822.5767	$822.59	$822.55	$822.60