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	$58.25	10.119%	$64.1443	$64.14	$64.15	$64.10
Purchase #2	$221.81	5.289%	$233.5415	$233.54	$233.55	$233.50
Purchase #3	$176.54	8.408%	$191.3835	$191.38	$191.40	$191.40
Purchase #4	$42.46	12.820%	$47.9034	$47.90	$47.90	$47.90
Purchase #5	$134.63	8.208%	$145.6804	$145.68	$145.70	$145.70
Purchase #6	$93.67	7.373%	$100.5763	$100.58	$100.60	$100.60
Purchase #7	$23.51	3.456%	$24.3225	$24.32	$24.30	$24.30
7 purchase totals =	$750.87		$807.5519	$807.54	$807.60	$807.50