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	$20.32	3.629%	$21.0574	$21.06	$21.05	$21.10
Purchase #2	$154.57	12.700%	$174.2004	$174.20	$174.20	$174.20
Purchase #3	$225.66	10.584%	$249.5439	$249.54	$249.55	$249.50
Purchase #4	$142.88	10.686%	$158.1482	$158.15	$158.15	$158.10
Purchase #5	$173.31	5.709%	$183.2043	$183.20	$183.20	$183.20
Purchase #6	$39.27	8.156%	$42.4729	$42.47	$42.45	$42.50
Purchase #7	$44.27	9.152%	$48.3216	$48.32	$48.30	$48.30
7 purchase totals =	$800.28		$876.9487	$876.94	$876.90	$876.90