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	$113.29	9.111%	$123.6119	$123.61	$123.60	$123.60
Purchase #2	$137.96	11.815%	$154.26	$154.26	$154.25	$154.30
Purchase #3	$233.70	9.262%	$255.3453	$255.35	$255.35	$255.30
Purchase #4	$6.32	13.331%	$7.1625	$7.16	$7.15	$7.20
Purchase #5	$136.45	3.733%	$141.5437	$141.54	$141.55	$141.50
Purchase #6	$45.71	4.244%	$47.6499	$47.65	$47.65	$47.60
Purchase #7	$109.64	9.816%	$120.4023	$120.40	$120.40	$120.40
7 purchase totals =	$783.07		$849.9756	$849.97	$849.95	$849.90