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	$110.51	7.102%	$118.3584	$118.36	$118.35	$118.40
Purchase #2	$154.66	12.246%	$173.5997	$173.60	$173.60	$173.60
Purchase #3	$56.34	7.240%	$60.419	$60.42	$60.40	$60.40
Purchase #4	$102.72	8.632%	$111.5868	$111.59	$111.60	$111.60
Purchase #5	$167.31	7.302%	$179.527	$179.53	$179.55	$179.50
Purchase #6	$37.85	9.640%	$41.4987	$41.50	$41.50	$41.50
Purchase #7	$214.76	5.214%	$225.9576	$225.96	$225.95	$226.00
7 purchase totals =	$844.15		$910.9472	$910.96	$910.95	$911.00