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	$21.51	13.485%	$24.4106	$24.41	$24.40	$24.40
Purchase #2	$136.47	11.821%	$152.6021	$152.60	$152.60	$152.60
Purchase #3	$183.49	3.591%	$190.0791	$190.08	$190.10	$190.10
Purchase #4	$57.61	5.549%	$60.8068	$60.81	$60.80	$60.80
Purchase #5	$155.28	10.320%	$171.3049	$171.30	$171.30	$171.30
Purchase #6	$29.92	8.705%	$32.5245	$32.52	$32.50	$32.50
Purchase #7	$9.74	13.196%	$11.0253	$11.03	$11.05	$11.00
7 purchase totals =	$594.02		$642.7533	$642.75	$642.75	$642.70