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	$159.47	12.141%	$178.8313	$178.83	$178.85	$178.80
Purchase #2	$250.56	8.182%	$271.0608	$271.06	$271.05	$271.10
Purchase #3	$114.25	3.507%	$118.2567	$118.26	$118.25	$118.30
Purchase #4	$68.94	13.534%	$78.2703	$78.27	$78.25	$78.30
Purchase #5	$131.80	3.133%	$135.9293	$135.93	$135.95	$135.90
Purchase #6	$12.45	3.505%	$12.8864	$12.89	$12.90	$12.90
Purchase #7	$132.77	9.279%	$145.0897	$145.09	$145.10	$145.10
7 purchase totals =	$870.24		$940.3245	$940.33	$940.35	$940.40