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	$65.33	8.211%	$70.6942	$70.69	$70.70	$70.70
Purchase #2	$142.43	11.556%	$158.8892	$158.89	$158.90	$158.90
Purchase #3	$152.67	5.380%	$160.8836	$160.88	$160.90	$160.90
Purchase #4	$227.68	7.300%	$244.3006	$244.30	$244.30	$244.30
Purchase #5	$145.84	9.689%	$159.9704	$159.97	$159.95	$160.00
Purchase #6	$11.89	3.301%	$12.2825	$12.28	$12.30	$12.30
Purchase #7	$40.90	6.380%	$43.5094	$43.51	$43.50	$43.50
7 purchase totals =	$786.74		$850.5299	$850.52	$850.55	$850.60