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	$163.61	12.641%	$184.2919	$184.29	$184.30	$184.30
Purchase #2	$108.77	10.723%	$120.4334	$120.43	$120.45	$120.40
Purchase #3	$131.93	13.570%	$149.8329	$149.83	$149.85	$149.80
Purchase #4	$103.72	7.613%	$111.6162	$111.62	$111.60	$111.60
Purchase #5	$186.62	4.721%	$195.4303	$195.43	$195.45	$195.40
Purchase #6	$161.57	3.270%	$166.8533	$166.85	$166.85	$166.90
Purchase #7	$171.38	11.312%	$190.7665	$190.77	$190.75	$190.80
7 purchase totals =	$1,027.60		$1,119.2245	$1,119.22	$1,119.25	$1,119.20