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	$179.53	6.574%	$191.3323	$191.33	$191.35	$191.30
Purchase #2	$89.85	5.182%	$94.506	$94.51	$94.50	$94.50
Purchase #3	$44.92	4.762%	$47.0591	$47.06	$47.05	$47.10
Purchase #4	$143.61	11.440%	$160.039	$160.04	$160.05	$160.00
Purchase #5	$74.81	10.548%	$82.701	$82.70	$82.70	$82.70
Purchase #6	$122.98	13.342%	$139.388	$139.39	$139.40	$139.40
Purchase #7	$249.87	5.413%	$263.3955	$263.40	$263.40	$263.40
7 purchase totals =	$905.57		$978.4209	$978.43	$978.45	$978.40