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	$39.94	9.768%	$43.8413	$43.84	$43.85	$43.80
Purchase #2	$90.91	10.287%	$100.2619	$100.26	$100.25	$100.30
Purchase #3	$133.70	4.150%	$139.2486	$139.25	$139.25	$139.20
Purchase #4	$122.71	3.831%	$127.411	$127.41	$127.40	$127.40
Purchase #5	$214.93	6.314%	$228.5007	$228.50	$228.50	$228.50
Purchase #6	$72.73	7.212%	$77.9753	$77.98	$78.00	$78.00
Purchase #7	$110.97	10.715%	$122.8604	$122.86	$122.85	$122.90
7 purchase totals =	$785.89		$840.0992	$840.10	$840.10	$840.10