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	$38.95	8.219%	$42.1513	$42.15	$42.15	$42.20
Purchase #2	$72.67	10.840%	$80.5474	$80.55	$80.55	$80.50
Purchase #3	$152.92	12.788%	$172.4754	$172.48	$172.50	$172.50
Purchase #4	$106.42	9.446%	$116.4724	$116.47	$116.45	$116.50
Purchase #5	$174.50	8.118%	$188.6659	$188.67	$188.65	$188.70
Purchase #6	$128.55	12.539%	$144.6689	$144.67	$144.65	$144.70
Purchase #7	$65.28	5.828%	$69.0845	$69.08	$69.10	$69.10
7 purchase totals =	$739.29		$814.0658	$814.07	$814.05	$814.20