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	$76.58	9.457%	$83.8222	$83.82	$83.80	$83.80
Purchase #2	$94.25	11.853%	$105.4215	$105.42	$105.40	$105.40
Purchase #3	$65.37	6.250%	$69.4556	$69.46	$69.45	$69.50
Purchase #4	$221.89	4.371%	$231.5888	$231.59	$231.60	$231.60
Purchase #5	$12.94	8.272%	$14.0104	$14.01	$14.00	$14.00
Purchase #6	$47.52	7.116%	$50.9015	$50.90	$50.90	$50.90
Purchase #7	$160.83	13.860%	$183.121	$183.12	$183.10	$183.10
7 purchase totals =	$679.38		$738.3210	$738.32	$738.25	$738.30