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	$184.70	6.487%	$196.6815	$196.68	$196.70	$196.70
Purchase #2	$227.94	13.542%	$258.8076	$258.81	$258.80	$258.80
Purchase #3	$108.57	8.738%	$118.0568	$118.06	$118.05	$118.10
Purchase #4	$75.82	12.653%	$85.4135	$85.41	$85.40	$85.40
Purchase #5	$189.42	8.441%	$205.4089	$205.41	$205.40	$205.40
Purchase #6	$126.61	12.641%	$142.6148	$142.61	$142.60	$142.60
Purchase #7	$250.50	13.530%	$284.3927	$284.39	$284.40	$284.40
7 purchase totals =	$1,163.56		$1,291.3758	$1,291.37	$1,291.35	$1,291.40