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	$186.89	12.416%	$210.0943	$210.09	$210.10	$210.10
Purchase #2	$171.35	11.243%	$190.6149	$190.61	$190.60	$190.60
Purchase #3	$116.80	5.411%	$123.12	$123.12	$123.10	$123.10
Purchase #4	$8.37	7.246%	$8.9765	$8.98	$9.00	$9.00
Purchase #5	$119.66	6.595%	$127.5516	$127.55	$127.55	$127.60
Purchase #6	$94.38	11.369%	$105.1101	$105.11	$105.10	$105.10
Purchase #7	$118.47	3.808%	$122.9813	$122.98	$123.00	$123.00
7 purchase totals =	$815.92		$888.4487	$888.44	$888.45	$888.50