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	$160.31	11.402%	$178.5885	$178.59	$178.60	$178.60
Purchase #2	$118.47	8.748%	$128.8338	$128.83	$128.85	$128.80
Purchase #3	$215.68	10.565%	$238.4666	$238.47	$238.45	$238.50
Purchase #4	$80.69	9.578%	$88.4185	$88.42	$88.40	$88.40
Purchase #5	$156.35	6.707%	$166.8364	$166.84	$166.85	$166.80
Purchase #6	$12.94	12.303%	$14.532	$14.53	$14.55	$14.50
Purchase #7	$217.99	11.663%	$243.4142	$243.41	$243.40	$243.40
7 purchase totals =	$962.43		$1,059.0900	$1,059.09	$1,059.10	$1,059.00