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	$138.71	4.159%	$144.4789	$144.48	$144.50	$144.50
Purchase #2	$70.82	13.597%	$80.4494	$80.45	$80.45	$80.40
Purchase #3	$39.29	4.681%	$41.1292	$41.13	$41.15	$41.10
Purchase #4	$57.30	6.718%	$61.1494	$61.15	$61.15	$61.10
Purchase #5	$105.30	8.510%	$114.261	$114.26	$114.25	$114.30
Purchase #6	$220.93	11.566%	$246.4828	$246.48	$246.50	$246.50
Purchase #7	$30.46	10.707%	$33.7214	$33.72	$33.70	$33.70
7 purchase totals =	$662.81		$721.6721	$721.67	$721.70	$721.60