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	$183.56	8.422%	$199.0194	$199.02	$199.00	$199.00
Purchase #2	$115.37	12.730%	$130.0566	$130.06	$130.05	$130.10
Purchase #3	$115.61	11.164%	$128.5167	$128.52	$128.50	$128.50
Purchase #4	$129.43	11.710%	$144.5863	$144.59	$144.60	$144.60
Purchase #5	$67.59	10.767%	$74.8674	$74.87	$74.85	$74.90
Purchase #6	$78.70	13.759%	$89.5283	$89.53	$89.55	$89.50
Purchase #7	$199.44	13.338%	$226.0413	$226.04	$226.05	$226.00
7 purchase totals =	$889.70		$992.6160	$992.63	$992.60	$992.60