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	$70.69	12.551%	$79.5623	$79.56	$79.55	$79.60
Purchase #2	$160.90	12.855%	$181.5837	$181.58	$181.60	$181.60
Purchase #3	$14.63	13.451%	$16.5979	$16.60	$16.60	$16.60
Purchase #4	$176.47	12.493%	$198.5164	$198.52	$198.50	$198.50
Purchase #5	$134.66	8.848%	$146.5747	$146.57	$146.55	$146.60
Purchase #6	$132.81	11.329%	$147.856	$147.86	$147.85	$147.90
Purchase #7	$54.38	9.384%	$59.483	$59.48	$59.50	$59.50
7 purchase totals =	$744.54		$830.1740	$830.17	$830.15	$830.30