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	$11.91	6.373%	$12.669	$12.67	$12.65	$12.70
Purchase #2	$92.86	6.116%	$98.5393	$98.54	$98.55	$98.50
Purchase #3	$154.53	4.528%	$161.5271	$161.53	$161.55	$161.50
Purchase #4	$43.86	3.470%	$45.3819	$45.38	$45.40	$45.40
Purchase #5	$211.94	12.412%	$238.246	$238.25	$238.25	$238.20
Purchase #6	$194.47	11.511%	$216.8554	$216.86	$216.85	$216.90
Purchase #7	$128.65	7.158%	$137.8588	$137.86	$137.85	$137.90
7 purchase totals =	$838.22		$911.0775	$911.09	$911.10	$911.10