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	$100.68	13.750%	$114.5235	$114.52	$114.50	$114.50
Purchase #2	$78.73	3.767%	$81.6958	$81.70	$81.70	$81.70
Purchase #3	$94.32	11.772%	$105.4234	$105.42	$105.40	$105.40
Purchase #4	$148.71	5.313%	$156.611	$156.61	$156.60	$156.60
Purchase #5	$103.93	6.419%	$110.6013	$110.60	$110.60	$110.60
Purchase #6	$50.39	6.786%	$53.8095	$53.81	$53.80	$53.80
Purchase #7	$18.89	6.538%	$20.125	$20.13	$20.15	$20.10
7 purchase totals =	$595.65		$642.7895	$642.79	$642.75	$642.70