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	$205.82	7.637%	$221.5385	$221.54	$221.55	$221.50
Purchase #2	$5.88	4.340%	$6.1352	$6.14	$6.15	$6.10
Purchase #3	$93.28	9.359%	$102.0101	$102.01	$102.00	$102.00
Purchase #4	$74.86	5.387%	$78.8927	$78.89	$78.90	$78.90
Purchase #5	$163.87	10.708%	$181.4172	$181.42	$181.40	$181.40
Purchase #6	$167.54	3.260%	$173.0018	$173.00	$173.00	$173.00
Purchase #7	$200.94	7.195%	$215.3976	$215.40	$215.40	$215.40
7 purchase totals =	$912.19		$978.3931	$978.40	$978.40	$978.30