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	$210.26	6.683%	$224.3117	$224.31	$224.30	$224.30
Purchase #2	$68.91	5.664%	$72.8131	$72.81	$72.80	$72.80
Purchase #3	$110.26	5.667%	$116.5084	$116.51	$116.50	$116.50
Purchase #4	$176.87	5.284%	$186.2158	$186.22	$186.20	$186.20
Purchase #5	$86.46	4.246%	$90.1311	$90.13	$90.15	$90.10
Purchase #6	$218.52	8.718%	$237.5706	$237.57	$237.55	$237.60
Purchase #7	$153.56	3.773%	$159.3538	$159.35	$159.35	$159.40
7 purchase totals =	$1,024.84		$1,086.9045	$1,086.90	$1,086.85	$1,086.90