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	$107.40	9.306%	$117.3946	$117.39	$117.40	$117.40
Purchase #2	$160.29	12.800%	$180.8071	$180.81	$180.80	$180.80
Purchase #3	$11.45	13.223%	$12.964	$12.96	$12.95	$13.00
Purchase #4	$90.46	10.104%	$99.6001	$99.60	$99.60	$99.60
Purchase #5	$42.63	7.252%	$45.7215	$45.72	$45.70	$45.70
Purchase #6	$12.48	6.383%	$13.2766	$13.28	$13.30	$13.30
Purchase #7	$136.32	12.791%	$153.7567	$153.76	$153.75	$153.80
7 purchase totals =	$561.03		$623.5206	$623.52	$623.50	$623.60