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	$88.25	12.242%	$99.0536	$99.05	$99.05	$99.10
Purchase #2	$158.43	12.717%	$178.5775	$178.58	$178.60	$178.60
Purchase #3	$199.85	13.734%	$227.2974	$227.30	$227.30	$227.30
Purchase #4	$172.61	7.235%	$185.0983	$185.10	$185.10	$185.10
Purchase #5	$185.77	12.436%	$208.8724	$208.87	$208.85	$208.90
Purchase #6	$20.95	11.518%	$23.363	$23.36	$23.35	$23.40
Purchase #7	$167.59	4.136%	$174.5215	$174.52	$174.50	$174.50
7 purchase totals =	$993.45		$1,096.7837	$1,096.78	$1,096.75	$1,096.90