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	$21.50	13.514%	$24.4055	$24.41	$24.40	$24.40
Purchase #2	$186.65	7.466%	$200.5853	$200.59	$200.60	$200.60
Purchase #3	$150.82	9.322%	$164.8794	$164.88	$164.90	$164.90
Purchase #4	$44.86	8.146%	$48.5143	$48.51	$48.50	$48.50
Purchase #5	$236.52	13.188%	$267.7123	$267.71	$267.70	$267.70
Purchase #6	$5.58	9.680%	$6.1201	$6.12	$6.10	$6.10
Purchase #7	$104.35	4.508%	$109.0541	$109.05	$109.05	$109.10
7 purchase totals =	$750.28		$821.2710	$821.27	$821.25	$821.30