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	$38.34	11.641%	$42.8032	$42.80	$42.80	$42.80
Purchase #2	$160.51	5.184%	$168.8308	$168.83	$168.85	$168.80
Purchase #3	$243.92	7.181%	$261.4359	$261.44	$261.45	$261.40
Purchase #4	$10.55	12.462%	$11.8647	$11.86	$11.85	$11.90
Purchase #5	$60.74	13.358%	$68.8536	$68.85	$68.85	$68.90
Purchase #6	$140.42	10.825%	$155.6205	$155.62	$155.60	$155.60
Purchase #7	$19.43	10.617%	$21.4929	$21.49	$21.50	$21.50
7 purchase totals =	$673.91		$730.9016	$730.89	$730.90	$730.90