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	$120.38	6.209%	$127.8544	$127.85	$127.85	$127.90
Purchase #2	$238.48	7.504%	$256.3755	$256.38	$256.40	$256.40
Purchase #3	$172.83	6.796%	$184.5755	$184.58	$184.60	$184.60
Purchase #4	$39.30	11.561%	$43.8435	$43.84	$43.85	$43.80
Purchase #5	$66.52	3.490%	$68.8415	$68.84	$68.85	$68.80
Purchase #6	$100.39	13.385%	$113.8272	$113.83	$113.85	$113.80
Purchase #7	$248.79	8.160%	$269.0913	$269.09	$269.10	$269.10
7 purchase totals =	$986.69		$1,064.4089	$1,064.41	$1,064.50	$1,064.40