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	$237.51	5.453%	$250.4614	$250.46	$250.45	$250.50
Purchase #2	$184.43	5.513%	$194.5976	$194.60	$194.60	$194.60
Purchase #3	$103.43	4.841%	$108.437	$108.44	$108.45	$108.40
Purchase #4	$40.85	3.559%	$42.3039	$42.30	$42.30	$42.30
Purchase #5	$157.65	12.517%	$177.3831	$177.38	$177.40	$177.40
Purchase #6	$78.42	5.516%	$82.7456	$82.75	$82.75	$82.70
Purchase #7	$131.60	9.302%	$143.8414	$143.84	$143.85	$143.80
7 purchase totals =	$933.89		$999.7700	$999.77	$999.80	$999.70