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	$91.64	12.582%	$103.1701	$103.17	$103.15	$103.20
Purchase #2	$14.26	11.703%	$15.9288	$15.93	$15.95	$15.90
Purchase #3	$19.33	13.291%	$21.8992	$21.90	$21.90	$21.90
Purchase #4	$197.60	11.156%	$219.6443	$219.64	$219.65	$219.60
Purchase #5	$34.69	13.598%	$39.4071	$39.41	$39.40	$39.40
Purchase #6	$119.82	13.871%	$136.4402	$136.44	$136.45	$136.40
Purchase #7	$50.54	5.321%	$53.2292	$53.23	$53.25	$53.20
7 purchase totals =	$527.88		$589.7189	$589.72	$589.75	$589.60