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	$124.35	10.636%	$137.5759	$137.58	$137.60	$137.60
Purchase #2	$136.92	4.598%	$143.2156	$143.22	$143.20	$143.20
Purchase #3	$151.88	13.699%	$172.686	$172.69	$172.70	$172.70
Purchase #4	$19.65	11.455%	$21.9009	$21.90	$21.90	$21.90
Purchase #5	$46.91	3.355%	$48.4838	$48.48	$48.50	$48.50
Purchase #6	$37.50	7.317%	$40.2439	$40.24	$40.25	$40.20
Purchase #7	$228.35	8.206%	$247.0884	$247.09	$247.10	$247.10
7 purchase totals =	$745.56		$811.1945	$811.20	$811.25	$811.20