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	$217.56	7.231%	$233.2918	$233.29	$233.30	$233.30
Purchase #2	$233.50	9.545%	$255.7876	$255.79	$255.80	$255.80
Purchase #3	$210.98	11.783%	$235.8398	$235.84	$235.85	$235.80
Purchase #4	$250.84	8.690%	$272.638	$272.64	$272.65	$272.60
Purchase #5	$114.87	10.691%	$127.1508	$127.15	$127.15	$127.20
Purchase #6	$105.81	12.745%	$119.2955	$119.30	$119.30	$119.30
Purchase #7	$28.52	11.625%	$31.8355	$31.84	$31.85	$31.80
7 purchase totals =	$1,162.08		$1,275.8390	$1,275.85	$1,275.90	$1,275.80