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	$229.50	9.651%	$251.649	$251.65	$251.65	$251.60
Purchase #2	$249.42	10.129%	$274.6838	$274.68	$274.70	$274.70
Purchase #3	$100.25	11.130%	$111.4078	$111.41	$111.40	$111.40
Purchase #4	$40.79	5.241%	$42.9278	$42.93	$42.95	$42.90
Purchase #5	$75.94	13.160%	$85.9337	$85.93	$85.95	$85.90
Purchase #6	$151.58	8.537%	$164.5204	$164.52	$164.50	$164.50
Purchase #7	$55.54	3.590%	$57.5339	$57.53	$57.55	$57.50
7 purchase totals =	$903.02		$988.6564	$988.65	$988.70	$988.50