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	$205.42	6.843%	$219.4769	$219.48	$219.50	$219.50
Purchase #2	$110.52	7.611%	$118.9317	$118.93	$118.95	$118.90
Purchase #3	$194.93	12.374%	$219.0506	$219.05	$219.05	$219.10
Purchase #4	$113.39	9.304%	$123.9398	$123.94	$123.95	$123.90
Purchase #5	$229.51	13.161%	$259.7158	$259.72	$259.70	$259.70
Purchase #6	$204.37	9.404%	$223.589	$223.59	$223.60	$223.60
Purchase #7	$47.31	11.716%	$52.8528	$52.85	$52.85	$52.90
7 purchase totals =	$1,105.45		$1,217.5566	$1,217.56	$1,217.60	$1,217.60