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	$38.65	9.817%	$42.4443	$42.44	$42.45	$42.40
Purchase #2	$49.42	5.416%	$52.0966	$52.10	$52.10	$52.10
Purchase #3	$149.77	12.522%	$168.5242	$168.52	$168.50	$168.50
Purchase #4	$188.76	5.121%	$198.4264	$198.43	$198.45	$198.40
Purchase #5	$212.89	13.583%	$241.8068	$241.81	$241.80	$241.80
Purchase #6	$180.53	3.325%	$186.5326	$186.53	$186.55	$186.50
Purchase #7	$128.43	13.776%	$146.1225	$146.12	$146.10	$146.10
7 purchase totals =	$948.45		$1,035.9534	$1,035.95	$1,035.95	$1,035.80