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	$204.64	8.208%	$221.4369	$221.44	$221.45	$221.40
Purchase #2	$241.72	6.156%	$256.6003	$256.60	$256.60	$256.60
Purchase #3	$185.86	10.224%	$204.8623	$204.86	$204.85	$204.90
Purchase #4	$19.85	7.870%	$21.4122	$21.41	$21.40	$21.40
Purchase #5	$123.95	3.175%	$127.8854	$127.89	$127.90	$127.90
Purchase #6	$212.70	9.228%	$232.328	$232.33	$232.35	$232.30
Purchase #7	$14.42	9.582%	$15.8017	$15.80	$15.80	$15.80
7 purchase totals =	$1,003.14		$1,080.3268	$1,080.33	$1,080.35	$1,080.30