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	$250.31	3.822%	$259.8768	$259.88	$259.90	$259.90
Purchase #2	$176.60	10.669%	$195.4415	$195.44	$195.45	$195.40
Purchase #3	$137.33	12.197%	$154.0801	$154.08	$154.10	$154.10
Purchase #4	$91.26	10.461%	$100.8067	$100.81	$100.80	$100.80
Purchase #5	$111.31	11.288%	$123.8747	$123.87	$123.85	$123.90
Purchase #6	$196.33	10.590%	$217.1213	$217.12	$217.10	$217.10
Purchase #7	$21.38	11.588%	$23.8575	$23.86	$23.85	$23.90
7 purchase totals =	$984.52		$1,075.0586	$1,075.06	$1,075.05	$1,075.10