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	$39.99	5.242%	$42.0863	$42.09	$42.10	$42.10
Purchase #2	$49.63	4.794%	$52.0093	$52.01	$52.00	$52.00
Purchase #3	$160.69	7.522%	$172.7771	$172.78	$172.80	$172.80
Purchase #4	$82.52	12.247%	$92.6262	$92.63	$92.65	$92.60
Purchase #5	$190.99	13.300%	$216.3917	$216.39	$216.40	$216.40
Purchase #6	$21.57	10.537%	$23.8428	$23.84	$23.85	$23.80
Purchase #7	$138.42	4.345%	$144.4343	$144.43	$144.45	$144.40
7 purchase totals =	$683.81		$744.1677	$744.17	$744.25	$744.10