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	$28.39	9.447%	$31.072	$31.07	$31.05	$31.10
Purchase #2	$230.94	6.151%	$245.1451	$245.15	$245.15	$245.10
Purchase #3	$157.56	8.597%	$171.1054	$171.11	$171.10	$171.10
Purchase #4	$108.55	3.725%	$112.5935	$112.59	$112.60	$112.60
Purchase #5	$80.90	7.830%	$87.2345	$87.23	$87.25	$87.20
Purchase #6	$172.28	12.766%	$194.2733	$194.27	$194.25	$194.30
Purchase #7	$95.42	5.657%	$100.8179	$100.82	$100.80	$100.80
7 purchase totals =	$874.04		$942.2417	$942.24	$942.20	$942.20