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	$230.81	4.636%	$241.5104	$241.51	$241.50	$241.50
Purchase #2	$138.27	5.754%	$146.2261	$146.23	$146.25	$146.20
Purchase #3	$144.81	7.387%	$155.5071	$155.51	$155.50	$155.50
Purchase #4	$94.73	6.769%	$101.1423	$101.14	$101.15	$101.10
Purchase #5	$162.41	8.573%	$176.3334	$176.33	$176.35	$176.30
Purchase #6	$19.67	6.193%	$20.8882	$20.89	$20.90	$20.90
Purchase #7	$51.87	13.720%	$58.9866	$58.99	$59.00	$59.00
7 purchase totals =	$842.57		$900.5941	$900.60	$900.65	$900.50