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	$220.33	3.848%	$228.8083	$228.81	$228.80	$228.80
Purchase #2	$215.48	3.806%	$223.6812	$223.68	$223.70	$223.70
Purchase #3	$109.90	11.434%	$122.466	$122.47	$122.45	$122.50
Purchase #4	$113.74	8.585%	$123.5046	$123.50	$123.50	$123.50
Purchase #5	$122.52	12.172%	$137.4331	$137.43	$137.45	$137.40
Purchase #6	$62.90	4.771%	$65.901	$65.90	$65.90	$65.90
Purchase #7	$214.44	3.201%	$221.3042	$221.30	$221.30	$221.30
7 purchase totals =	$1,059.31		$1,123.0984	$1,123.09	$1,123.10	$1,123.10