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	$200.33	6.260%	$212.8707	$212.87	$212.85	$212.90
Purchase #2	$153.84	3.690%	$159.5167	$159.52	$159.50	$159.50
Purchase #3	$126.95	7.606%	$136.6058	$136.61	$136.60	$136.60
Purchase #4	$118.33	3.418%	$122.3745	$122.37	$122.35	$122.40
Purchase #5	$187.67	4.791%	$196.6613	$196.66	$196.65	$196.70
Purchase #6	$29.57	5.590%	$31.223	$31.22	$31.20	$31.20
Purchase #7	$152.43	4.291%	$158.9708	$158.97	$158.95	$159.00
7 purchase totals =	$969.12		$1,018.2228	$1,018.22	$1,018.10	$1,018.30