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	$80.98	8.372%	$87.7596	$87.76	$87.75	$87.80
Purchase #2	$149.59	3.710%	$155.1398	$155.14	$155.15	$155.10
Purchase #3	$123.57	6.857%	$132.0432	$132.04	$132.05	$132.00
Purchase #4	$181.94	4.669%	$190.4348	$190.43	$190.45	$190.40
Purchase #5	$114.85	7.538%	$123.5074	$123.51	$123.50	$123.50
Purchase #6	$90.69	7.721%	$97.6922	$97.69	$97.70	$97.70
Purchase #7	$48.34	13.381%	$54.8084	$54.81	$54.80	$54.80
7 purchase totals =	$789.96		$841.3854	$841.38	$841.40	$841.30