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	$70.81	10.484%	$78.2337	$78.23	$78.25	$78.20
Purchase #2	$144.66	5.369%	$152.4268	$152.43	$152.45	$152.40
Purchase #3	$175.84	9.737%	$192.9615	$192.96	$192.95	$193.00
Purchase #4	$38.52	5.324%	$40.5708	$40.57	$40.55	$40.60
Purchase #5	$20.56	3.750%	$21.331	$21.33	$21.35	$21.30
Purchase #6	$37.68	7.687%	$40.5765	$40.58	$40.60	$40.60
Purchase #7	$6.55	7.163%	$7.0192	$7.02	$7.00	$7.00
7 purchase totals =	$494.62		$533.1195	$533.12	$533.15	$533.10