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	$229.91	12.262%	$258.1016	$258.10	$258.10	$258.10
Purchase #2	$68.97	10.818%	$76.4312	$76.43	$76.45	$76.40
Purchase #3	$72.76	13.462%	$82.555	$82.56	$82.55	$82.60
Purchase #4	$152.69	7.381%	$163.96	$163.96	$163.95	$164.00
Purchase #5	$115.99	10.113%	$127.7201	$127.72	$127.70	$127.70
Purchase #6	$58.60	5.128%	$61.605	$61.61	$61.60	$61.60
Purchase #7	$177.60	6.759%	$189.604	$189.60	$189.60	$189.60
7 purchase totals =	$876.52		$959.9769	$959.98	$959.95	$960.00