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	$139.27	6.658%	$148.5426	$148.54	$148.55	$148.50
Purchase #2	$59.56	7.288%	$63.9007	$63.90	$63.90	$63.90
Purchase #3	$155.30	11.139%	$172.5989	$172.60	$172.60	$172.60
Purchase #4	$143.42	8.558%	$155.6939	$155.69	$155.70	$155.70
Purchase #5	$199.46	7.561%	$214.5412	$214.54	$214.55	$214.50
Purchase #6	$93.45	8.182%	$101.0961	$101.10	$101.10	$101.10
Purchase #7	$96.26	12.480%	$108.2732	$108.27	$108.25	$108.30
7 purchase totals =	$886.72		$964.6466	$964.64	$964.65	$964.60