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	$159.73	12.245%	$179.2889	$179.29	$179.30	$179.30
Purchase #2	$154.61	13.415%	$175.3509	$175.35	$175.35	$175.40
Purchase #3	$115.77	9.323%	$126.5632	$126.56	$126.55	$126.60
Purchase #4	$107.66	6.758%	$114.9357	$114.94	$114.95	$114.90
Purchase #5	$140.27	10.193%	$154.5677	$154.57	$154.55	$154.60
Purchase #6	$18.31	11.583%	$20.4308	$20.43	$20.45	$20.40
Purchase #7	$132.87	7.187%	$142.4194	$142.42	$142.40	$142.40
7 purchase totals =	$829.22		$913.5566	$913.56	$913.55	$913.60