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	$80.51	3.647%	$83.4462	$83.45	$83.45	$83.40
Purchase #2	$127.28	9.862%	$139.8324	$139.83	$139.85	$139.80
Purchase #3	$111.93	8.781%	$121.7586	$121.76	$121.75	$121.80
Purchase #4	$91.70	9.212%	$100.1474	$100.15	$100.15	$100.10
Purchase #5	$76.88	11.350%	$85.6059	$85.61	$85.60	$85.60
Purchase #6	$58.62	3.149%	$60.4659	$60.47	$60.45	$60.50
Purchase #7	$176.98	9.805%	$194.3329	$194.33	$194.35	$194.30
7 purchase totals =	$723.90		$785.5893	$785.60	$785.60	$785.50