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	$77.82	3.463%	$80.5149	$80.51	$80.50	$80.50
Purchase #2	$153.75	13.477%	$174.4709	$174.47	$174.45	$174.50
Purchase #3	$45.99	5.367%	$48.4583	$48.46	$48.45	$48.50
Purchase #4	$10.47	11.206%	$11.6433	$11.64	$11.65	$11.60
Purchase #5	$33.30	13.698%	$37.8614	$37.86	$37.85	$37.90
Purchase #6	$139.73	7.569%	$150.3062	$150.31	$150.30	$150.30
Purchase #7	$7.96	11.156%	$8.848	$8.85	$8.85	$8.80
7 purchase totals =	$469.02		$512.1030	$512.10	$512.05	$512.10