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	$117.45	12.752%	$132.4272	$132.43	$132.45	$132.40
Purchase #2	$171.25	7.404%	$183.9294	$183.93	$183.95	$183.90
Purchase #3	$151.98	6.711%	$162.1794	$162.18	$162.20	$162.20
Purchase #4	$162.91	9.816%	$178.9012	$178.90	$178.90	$178.90
Purchase #5	$49.53	7.145%	$53.0689	$53.07	$53.05	$53.10
Purchase #6	$45.62	6.241%	$48.4671	$48.47	$48.45	$48.50
Purchase #7	$166.71	4.566%	$174.322	$174.32	$174.30	$174.30
7 purchase totals =	$865.45		$933.2952	$933.30	$933.30	$933.30