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	$73.25	10.796%	$81.1581	$81.16	$81.15	$81.20
Purchase #2	$144.60	11.367%	$161.0367	$161.04	$161.05	$161.00
Purchase #3	$91.47	9.870%	$100.4981	$100.50	$100.50	$100.50
Purchase #4	$96.40	11.533%	$107.5178	$107.52	$107.50	$107.50
Purchase #5	$166.64	8.832%	$181.3576	$181.36	$181.35	$181.40
Purchase #6	$80.39	12.617%	$90.5328	$90.53	$90.55	$90.50
Purchase #7	$120.77	11.700%	$134.9001	$134.90	$134.90	$134.90
7 purchase totals =	$773.52		$857.0012	$857.01	$857.00	$857.00