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	$40.61	12.828%	$45.8195	$45.82	$45.80	$45.80
Purchase #2	$215.87	10.660%	$238.8817	$238.88	$238.90	$238.90
Purchase #3	$178.92	7.371%	$192.1082	$192.11	$192.10	$192.10
Purchase #4	$32.25	4.231%	$33.6145	$33.61	$33.60	$33.60
Purchase #5	$194.43	10.529%	$214.9015	$214.90	$214.90	$214.90
Purchase #6	$30.89	4.660%	$32.3295	$32.33	$32.35	$32.30
Purchase #7	$103.65	3.427%	$107.2021	$107.20	$107.20	$107.20
7 purchase totals =	$796.62		$864.8570	$864.85	$864.85	$864.80