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	$50.80	13.387%	$57.6006	$57.60	$57.60	$57.60
Purchase #2	$145.39	4.695%	$152.2161	$152.22	$152.20	$152.20
Purchase #3	$67.29	5.820%	$71.2063	$71.21	$71.20	$71.20
Purchase #4	$41.64	4.255%	$43.4118	$43.41	$43.40	$43.40
Purchase #5	$155.89	5.235%	$164.0508	$164.05	$164.05	$164.10
Purchase #6	$17.27	7.657%	$18.5924	$18.59	$18.60	$18.60
Purchase #7	$69.97	9.249%	$76.4415	$76.44	$76.45	$76.40
7 purchase totals =	$548.25		$583.5195	$583.52	$583.50	$583.50