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	$181.99	13.103%	$205.8361	$205.84	$205.85	$205.80
Purchase #2	$102.80	10.223%	$113.3092	$113.31	$113.30	$113.30
Purchase #3	$112.88	7.135%	$120.934	$120.93	$120.95	$120.90
Purchase #4	$82.80	9.260%	$90.4673	$90.47	$90.45	$90.50
Purchase #5	$152.52	5.239%	$160.5105	$160.51	$160.50	$160.50
Purchase #6	$78.53	3.120%	$80.9801	$80.98	$81.00	$81.00
Purchase #7	$31.77	5.732%	$33.5911	$33.59	$33.60	$33.60
7 purchase totals =	$743.29		$805.6283	$805.63	$805.65	$805.60