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	$210.28	9.569%	$230.4017	$230.40	$230.40	$230.40
Purchase #2	$102.91	11.656%	$114.9052	$114.91	$114.90	$114.90
Purchase #3	$217.60	8.697%	$236.5247	$236.52	$236.50	$236.50
Purchase #4	$183.90	4.160%	$191.5502	$191.55	$191.55	$191.60
Purchase #5	$111.50	6.536%	$118.7876	$118.79	$118.80	$118.80
Purchase #6	$152.37	9.780%	$167.2718	$167.27	$167.25	$167.30
Purchase #7	$142.91	9.234%	$156.1063	$156.11	$156.10	$156.10
7 purchase totals =	$1,121.47		$1,215.5475	$1,215.55	$1,215.50	$1,215.60